Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation

<!DOCTYPE html> <html lang="en" > <head > <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="HandheldFriendly" content="True" /> <meta name="MobileOptimized" content="320" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <link rel="stylesheet" href="/static/assets/style-70b9163a.css" /> <script type="module" crossorigin="" src="/static/assets/base_style-ec2bc71e.js"></script> <link rel="stylesheet" href="/static/assets/style-ef962842.css" /> <link rel="stylesheet" href="/static/assets/style-3ade8b5c.css" /> <script type="module" crossorigin="" src="/static/assets/article_style-d757a0dd.js"></script> <style> @media screen and (min-width: 64em) { div.pmc-wm { background: repeat-y; background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='20' height='350' xmlns:xlink='http://www.w3.org/1999/xlink'%3E%3Cdefs%3E%3Cfilter x='-.02' y='0' width='1.05' height='1' id='c'%3E%3CfeFlood flood-color='%23FFF'/%3E%3CfeComposite in='SourceGraphic'/%3E%3C/filter%3E%3Ctext id='b' font-family='Helvetica' font-size='11pt' style='opacity:1;fill:%23005ea2;stroke:none;text-anchor:middle' x='175' y='14'%3E%3C/text%3E%3Cpath id='a' style='fill:%23005ea2' d='M0 8h350v3H0z'/%3E%3C/defs%3E%3Cuse xlink:href='%23a' transform='rotate(90 10 10)'/%3E%3Cuse xlink:href='%23b' transform='rotate(90 10 10)' filter='url(%23c)'/%3E%3C/svg%3E"); padding-left: 3rem; } } </style> <link rel="apple-touch-icon" sizes="180x180" href="/static/img/favicons/apple-touch-icon.png" /> <link rel="icon" type="image/png" sizes="48x48" href="/static/img/favicons/favicon-48x48.png" /> <link rel="icon" type="image/png" sizes="32x32" href="/static/img/favicons/favicon-32x32.png" /> <link rel="icon" type="image/png" sizes="16x16" href="/static/img/favicons/favicon-16x16.png" /> <link rel="manifest" href="/static/img/favicons/site.webmanifest" /> <link rel="mask-icon" href="/static/img/favicons/safari-pinned-tab.svg" color="#0071bc" /> <meta name="msapplication-config" content="/static/img/favicons/browserconfig.xml" /> <meta name="theme-color" content="#ffffff" /> <title> Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation - PMC </title>  <meta name="ncbi_app" content="cloudpmc-viewer" /> <meta name="ncbi_db" content="pmc" /> <meta name="ncbi_phid" content="E5FDB9C0750362930AB9C000443073E6.m_1" />  <meta name="ncbi_pdid" content="article" /> <link rel="preconnect" href="https://www.google-analytics.com" /> <link rel="dns-prefetch" href="https://cdn.ncbi.nlm.nih.gov" /> <link rel="preconnect" href="https://code.jquery.com" /> <meta name="ncbi_domain" content="plosone"> <meta name="ncbi_type" content="fulltext"> <meta name="ncbi_pcid" content="journal"> <link rel="canonical" href="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/"> <meta name="robots" content="INDEX,NOFOLLOW,NOARCHIVE"> <meta name="citation_journal_title" content="PLoS ONE"> <meta name="citation_title" content="Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation"> <meta name="citation_author" content="Gregory M Erickson"> <meta name="citation_author_institution" content="Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America"> <meta name="citation_author" content="Paul M Gignac"> <meta name="citation_author_institution" content="Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America"> <meta name="citation_author" content="Scott J Steppan"> <meta name="citation_author_institution" content="Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America"> <meta name="citation_author" content="A Kristopher Lappin"> <meta name="citation_author_institution" content="Biological Sciences Department, California State Polytechnic University, Pomona, California, United States of America"> <meta name="citation_author" content="Kent A Vliet"> <meta name="citation_author_institution" content="Department of Biology, University of Florida, Gainesville, Florida, United States of America"> <meta name="citation_author" content="John D Brueggen"> <meta name="citation_author_institution" content="St. Augustine Alligator Farm Zoological Park, St. Augustine, Florida, United States of America"> <meta name="citation_author" content="Brian D Inouye"> <meta name="citation_author_institution" content="Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America"> <meta name="citation_author" content="David Kledzik"> <meta name="citation_author_institution" content="St. Augustine Alligator Farm Zoological Park, St. Augustine, Florida, United States of America"> <meta name="citation_author" content="Grahame J W Webb"> <meta name="citation_author_institution" content="Wildlife Management International, Karama, and School of Environmental Research, Charles Darwin University, Darwin, Northern Territories, Australia"> <meta name="citation_publication_date" content="2012 Mar 14"> <meta name="citation_volume" content="7"> <meta name="citation_issue" content="3"> <meta name="citation_firstpage" content="e31781"> <meta name="citation_doi" content="10.1371/journal.pone.0031781"> <meta name="citation_pmid" content="22431965"> <meta name="citation_abstract_html_url" content="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/"> <meta name="citation_fulltext_html_url" content="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/"> <meta name="citation_pdf_url" content="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/pdf/pone.0031781.pdf"> <meta name="description" content="Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often ..."> <meta name="og:title" content="Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation"> <meta name="og:type" content="article"> <meta name="og:site_name" content="PubMed Central (PMC)"> <meta name="og:description" content="Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often ..."> <meta name="og:url" content="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/"> <meta name="og:image" content="https://cdn.ncbi.nlm.nih.gov/pmc/cms/images/pmc-card-share.jpg?_=0"> <meta name="twitter:card" content="summary_large_image"> <meta name="twitter:site" content="@ncbi"> </head> <body > <a class="usa-skipnav " href="#main-content"> Skip to main content </a> <section class="usa-banner " aria-label="Official website of the United States government" > <div class="usa-accordion"> <header class="usa-banner__header"> <div class="usa-banner__inner"> <div class="grid-col-auto"> <img aria-hidden="true" class="usa-banner__header-flag" src="/static/img/us_flag.svg" alt="" /> </div> <div class="grid-col-fill tablet:grid-col-auto" aria-hidden="true"> <p class="usa-banner__header-text"> An official website of the United States government </p> <span class="usa-banner__header-action">Here's how you know</span> </div> <button type="button" class="usa-accordion__button usa-banner__button " aria-expanded="false" aria-controls="gov-banner-default" data-testid="storybook-django-banner" > <span class="usa-banner__button-text">Here's how you know</span> </button> </div> </header> <div class="usa-banner__content usa-accordion__content" id="gov-banner-default" hidden> <div class="grid-row grid-gap-lg"> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="/static/img/icon-dot-gov.svg" alt="" aria-hidden="true" /> <div class="usa-media-block__body"> <p> <strong>Official websites use .gov</strong> <br /> A <strong>.gov</strong> website belongs to an official government organization in the United States. </p> </div> </div> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="/static/img/icon-https.svg" alt="" aria-hidden="true" /> <div class="usa-media-block__body"> <p> <strong>Secure .gov websites use HTTPS</strong> <br /> A <strong>lock</strong> ( <span class="icon-lock"> <svg xmlns="http://www.w3.org/2000/svg" width="52" height="64" viewBox="0 0 52 64" class="usa-banner__lock-image" role="graphics-symbol" aria-labelledby="banner-lock-description" focusable="false"> <title id="banner-lock-title">Lock</title> <desc id="banner-lock-description"> Locked padlock icon </desc> <path fill="#000000" fill-rule="evenodd" d="M26 0c10.493 0 19 8.507 19 19v9h3a4 4 0 0 1 4 4v28a4 4 0 0 1-4 4H4a4 4 0 0 1-4-4V32a4 4 0 0 1 4-4h3v-9C7 8.507 15.507 0 26 0zm0 8c-5.979 0-10.843 4.77-10.996 10.712L15 19v9h22v-9c0-6.075-4.925-11-11-11z" /> </svg> </span>) or <strong>https://</strong> means you've safely connected to the .gov website. Share sensitive information only on official, secure websites. </p> </div> </div> </div> </div> </div> </section> <div class="usa-overlay"> </div> <header class="usa-header usa-header--extended usa-header--wide" data-testid="header" data-header > <div class="ncbi-header"> <div class="ncbi-header__container"> <a class="ncbi-header__logo-container" href="/"> <img alt=" PMC home page " class="ncbi-header__logo-image" src="/static/img/ncbi-logos/nih-nlm-ncbi--white.svg" /> </a>  <button type="button" class="usa-menu-btn ncbi-header__hamburger-button " aria-label="Show menu" data-testid="navMenuButton" > <svg aria-hidden="true" class="ncbi-hamburger-icon" fill="none" focusable="false" height="21" viewBox="0 0 31 21" width="31" xmlns="http://www.w3.org/2000/svg"> <path clip-rule="evenodd" d="M0.125 20.75H30.875V17.3333H0.125V20.75ZM0.125 12.2083H30.875V8.79167H0.125V12.2083ZM0.125 0.25V3.66667H30.875V0.25H0.125Z" fill="#F1F1F1" fill-rule="evenodd" /> </svg> </button>  <div class="ncbi-header__desktop-buttons">  <button type="button" class="usa-button usa-button--unstyled ncbi-header__desktop-button " aria-expanded="false" aria-controls="search-field-desktop-navigation" aria-label="Show search overlay" data-testid="toggleSearchPanelButton" data-toggle-search-panel-button > <svg class="usa-icon " role="graphics-symbol" aria-hidden="true" > <use xlink:href="/static/img/sprite.svg#search" /> </svg> Search </button>  <div class="ncbi-header__login-dropdown"> <button type="button" class="usa-button usa-button--unstyled ncbi-header__desktop-button ncbi-header__login-dropdown-button " aria-expanded="false" aria-controls="login-dropdown-menu" aria-label="Show login menu" data-testid="toggleLoginMenuDropdown" data-desktop-login-button > <svg class="usa-icon " role="graphics-symbol" aria-hidden="true" > <use xlink:href="/static/img/sprite.svg#person" /> </svg> <span data-login-dropdown-text>Log in</span>  <svg class="usa-icon ncbi-header__login-dropdown-icon ncbi-header__login-dropdown-icon--expand-less ncbi-header__login-dropdown-icon--hidden" role="graphics-symbol" aria-hidden="true" data-login-dropdown-up-arrow> <use xlink:href="/static/img/sprite.svg#expand_less" /> </svg>  <svg class="usa-icon ncbi-header__login-dropdown-icon ncbi-header__login-dropdown-icon--expand-more ncbi-header__login-dropdown-icon--hidden" role="graphics-symbol" aria-hidden="true" data-login-dropdown-down-arrow> <use xlink:href="/static/img/sprite.svg#expand_more" /> </svg> </button>  <ul class="usa-nav__submenu ncbi-header__login-dropdown-menu" id="login-dropdown-menu" data-desktop-login-menu-dropdown hidden> <li class="usa-nav__submenu-item">  <a href="https://www.ncbi.nlm.nih.gov/myncbi/" class="usa-link " > Dashboard </a> </li> <li class="usa-nav__submenu-item">  <a href="https://www.ncbi.nlm.nih.gov/myncbi/collections/bibliography/" class="usa-link " > Publications </a> </li> <li class="usa-nav__submenu-item">  <a href="https://www.ncbi.nlm.nih.gov/account/settings/" class="usa-link " > Account settings </a> </li> <li class="usa-nav__submenu-item"> <button type="button" class="usa-button usa-button--outline ncbi-header__login-dropdown-logout-button " data-testid="desktopLogoutButton" data-desktop-logout-button > Log out </button> </li> </ul> </div> </div> </div> </div>  <div class="ncbi-search-panel ncbi--show-only-at-desktop" data-testid="searchPanel" data-header-search-panel hidden> <div class="ncbi-search-panel__container"> <form action="https://www.ncbi.nlm.nih.gov/search/all/" aria-describedby="search-field-desktop-navigation-help-text" autocomplete="off" class="usa-search usa-search--big ncbi-search-panel__form" data-testid="form" method="GET" role="search"> <label class="usa-sr-only" data-testid="label" for="search-field-desktop-navigation"> Search… </label> <input class="usa-input" data-testid="textInput" id="search-field-desktop-navigation" name="term" placeholder="Search NCBI" type="search" value="" /> <button type="submit" class="usa-button " data-testid="button" > <span class="usa-search__submit-text"> Search NCBI </span> </button> </form> </div> </div> <nav aria-label="Primary navigation" class="usa-nav"> <p class="usa-sr-only" id="primary-navigation-sr-only-title"> Primary site navigation </p>  <button type="button" class="usa-nav__close ncbi-nav__close-button " aria-label="Close navigation menu" data-testid="navCloseButton" > <img src="/static/img/usa-icons/close.svg" alt="Close" /> </button>  <form class="usa-search usa-search--small ncbi--hide-at-desktop margin-top-6" role="search"> <label class="usa-sr-only" for="search-field"> Search </label> <input class="usa-input" id="search-field-mobile-navigation" type="search" placeholder="Search NCBI" name="search" /> <button type="submit" class="usa-button " >  <img src="data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIGhlaWdodD0iMjQiIHZpZXdCb3g9IjAgMCAyNCAyNCIgd2lkdGg9IjI0Ij48cGF0aCBkPSJNMCAwaDI0djI0SDB6IiBmaWxsPSJub25lIi8+PHBhdGggZmlsbD0iI2ZmZiIgZD0iTTE1LjUgMTRoLS43OWwtLjI4LS4yN0E2LjQ3MSA2LjQ3MSAwIDAgMCAxNiA5LjUgNi41IDYuNSAwIDEgMCA5LjUgMTZjMS42MSAwIDMuMDktLjU5IDQuMjMtMS41N2wuMjcuMjh2Ljc5bDUgNC45OUwyMC40OSAxOWwtNC45OS01em0tNiAwQzcuMDEgMTQgNSAxMS45OSA1IDkuNVM3LjAxIDUgOS41IDUgMTQgNy4wMSAxNCA5LjUgMTEuOTkgMTQgOS41IDE0eiIvPjwvc3ZnPg==" class="usa-search__submit-icon" alt="Search" /> </button> </form>   <div class="ncbi-nav__mobile-login-menu ncbi--hide-at-desktop" data-mobile-login-menu hidden> <p class="ncbi-nav__mobile-login-menu-status"> Logged in as: <strong class="ncbi-nav__mobile-login-menu-email" data-mobile-login-email-text></strong> </p> <ul class="usa-nav__primary usa-accordion"> <li class="usa-nav__primary-item"> <a href="https://www.ncbi.nlm.nih.gov/myncbi/" class="usa-link " > Dashboard </a> </li> <li class="usa-nav__primary-item"> <a href="https://www.ncbi.nlm.nih.gov/myncbi/collections/bibliography/" class="usa-link " > Publications </a> </li> <li class="usa-nav__primary-item"> <a href="https://www.ncbi.nlm.nih.gov/account/settings/" class="usa-link " > Account settings </a> </li> </ul> </div> <button type="button" class="usa-button ncbi-nav__mobile-login-button ncbi--hide-at-desktop " data-testid="mobileLoginButton" data-mobile-login-button > Log in </button> </nav> </header> <section class="pmc-header pmc-header--basic" aria-label="PMC Header with search box"> <div class="pmc-nav-container"> <div class="pmc-header__bar"> <div class="pmc-header__logo"> <a href="/" title="Home" aria-label="PMC Home"></a> </div> <button type="button" class="usa-button usa-button--unstyled pmc-header__search__button" aria-label="Open search" data-ga-category="search" data-ga-action="PMC" data-ga-label="pmc_search_panel_mobile" > <svg class="usa-icon width-4 height-4 pmc-icon__open" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#search"></use> </svg> <svg class="usa-icon width-4 height-4 pmc-icon__close" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#close"></use> </svg> </button> </div> <div class="pmc-header__search"> <form class="usa-search usa-search--extra usa-search--article-right-column pmc-header__search__form" autocomplete="off" role="search"> <label class="usa-sr-only" for="pmc-search">Search PMC Full-Text Archive</label> <span class="autoComplete_wrapper flex-1"> <input class="usa-input width-full maxw-none" required="required" placeholder="Search PMC Full-Text Archive" id="pmc-search" type="search" name="term" data-autocomplete-url="/search/autocomplete/"/> </span> <button class="usa-button" type="submit" formaction="https://www.ncbi.nlm.nih.gov/pmc/" data-ga-category="search" data-ga-action="PMC" data-ga-label="PMC_search_button" > <span class="usa-search__submit-text">Search in PMC</span> <img src="/static/img/usa-icons-bg/search--white.svg" class="usa-search__submit-icon" alt="Search" /> </button> </form> <ul class="pmc-header__search__menu"> <li> <a class="usa-link" href="https://www.ncbi.nlm.nih.gov/pmc/advanced/" data-ga-action="featured_link" data-ga-label="advanced_search"> Advanced Search </a> </li> <li> <a class="usa-link" href="/journals/" data-ga-action="featured_link" data-ga-label="journal list"> Journal List </a> </li> <li> <a class="usa-link" href="/about/userguide/" data-ga-action="featured_link" data-ga-label="user guide"> User Guide </a> </li> </ul> </div> </div> </section> <div class="usa-section padding-top-0 desktop:padding-top-6 pmc-article-section" data-article-db="pmc" data-article-id="3303775"> <div class="grid-container pmc-actions-bar" aria-label="Actions bar" role="complementary"> <div class="grid-row"> <div class="grid-col-fill display-flex"> <div class="display-flex"> <ul class="usa-list usa-list--unstyled usa-list--horizontal"> <li class="margin-right-2 mobile-lg:margin-right-4 display-flex mob"> <button type="button" class="usa-button pmc-sidenav__container__open usa-button--unstyled width-auto display-flex" aria-label="Open resources" data-extra-class="is-visible-resources" data-ga-category="resources_accordion" data-ga-action="click" data-ga-label="mobile_icon" > <svg class="usa-icon width-4 height-4" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#more_vert"></use> </svg> </button> </li> <li class="margin-right-2 mobile-lg:margin-right-4 display-flex mob"> <a href="https://doi.org/10.1371/journal.pone.0031781" class="usa-link display-flex" role="button" target="_blank" rel="noreferrer noopener" aria-label="View on publisher site" data-ga-category="actions" data-ga-action="click" data-ga-label="publisher_link_mobile" > <svg class="usa-icon width-4 height-4" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#launch"></use> </svg> </a> </li> <li class="margin-right-2 mobile-lg:margin-right-4 display-flex"> <a href="pdf/pone.0031781.pdf" class="usa-link display-flex" role="button" aria-label="Download PDF" data-ga-category="actions" data-ga-action="click" data-ga-label="pdf_download_mobile" > <svg class="usa-icon width-4 height-4" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#file_download"></use> </svg> </a> </li> <li class="margin-right-2 mobile-lg:margin-right-4 display-flex"> <button class="usa-button usa-button--unstyled collections-dialog-trigger collections-button display-flex collections-button-empty" aria-label="Save article in MyNCBI collections." data-ga-category="actions" data-ga-action="click" data-ga-label="collections_button_mobile" data-collections-open-dialog-enabled="false" data-collections-open-dialog-url="https://account.ncbi.nlm.nih.gov/?back_url=https%3A%2F%2Fpmc.ncbi.nlm.nih.gov%2Farticles%2FPMC3303775%2F%23open-collections-dialog" data-in-collections="false" > <svg class="usa-icon width-4 height-4 usa-icon--bookmark-full" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/action-bookmark-full.svg#icon"></use> </svg> <svg class="usa-icon width-4 height-4 usa-icon--bookmark-empty" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/action-bookmark-empty.svg#icon"></use> </svg> </button> </li> <li class="margin-right-2 mobile-lg:margin-right-4 display-flex"> <button role="button" class="usa-button usa-button--unstyled citation-dialog-trigger display-flex" aria-label="Open dialog with citation text in different styles" data-ga-category="actions" data-ga-action="open" data-ga-label="cite_mobile" data-all-citations-url="/resources/citations/3303775/" data-citation-style="nlm" data-download-format-link="/resources/citations/3303775/export/" > <svg class="usa-icon width-4 height-4 usa-icon--bookmark-empty" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/sprite.svg#format_quote"></use> </svg> </button> </li> <li class="pmc-permalink display-flex"> <button type="button" class="usa-button usa-button--unstyled display-flex" aria-label="Show article permalink" aria-expanded="false" aria-haspopup="true" data-ga-category="actions" data-ga-action="open" data-ga-label="permalink_mobile" > <svg class="usa-icon width-4 height-4" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#share"></use> </svg> </button> <div class="pmc-permalink__dropdown" hidden> <div class="pmc-permalink__dropdown__container"> <h2 class="usa-modal__heading margin-top-0 margin-bottom-2">PERMALINK</h2> <div class="pmc-permalink__dropdown__content"> <input type="text" class="usa-input" value="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/" aria-label="Article permalink"> <button class="usa-button display-inline-flex pmc-permalink__dropdown__copy__btn margin-right-0" title="Copy article permalink" data-ga-category="save_share" data-ga-action="link" data-ga-label="copy_link"> <svg class="usa-icon" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#content_copy"></use> </svg> <span class="margin-left-1">Copy</span> </button> </div> </div> </div> </li> </ul> </div> <button type="button" class="usa-button pmc-sidenav__container__open usa-button--unstyled width-auto display-flex" aria-label="Open article navigation" data-extra-class="is-visible-in-page" data-ga-category="actions" data-ga-action="open" data-ga-label="article_nav_mobile" > <svg class="usa-icon width-4 height-4" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#list"></use> </svg> </button> </div> </div> </div> <div class="grid-container desktop:padding-left-6"> <div id="article-container" class="grid-row grid-gap"> <div class="grid-col-12 desktop:grid-col-8 order-2 pmc-layout__content"> <div class="grid-container padding-left-0 padding-right-0"> <div class="grid-row desktop:margin-left-neg-6"> <div class="grid-col-12"> <div class="pmc-layout__disclaimer" role="complementary" aria-label="Disclaimer note"> As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health.<br/> Learn more: <a class="usa-link" data-ga-category="Link click" data-ga-action="Disclaimer" data-ga-label="New disclaimer box" href="/about/disclaimer/">PMC Disclaimer</a> | <a class="usa-link" data-ga-category="Link click" data-ga-action="PMC Copyright Notice" data-ga-label="New disclaimer box" href="/about/copyright/"> PMC Copyright Notice </a> </div> </div> </div> <div class="grid-row pmc-wm desktop:margin-left-neg-6">  <main id="main-content" class="usa-layout-docs__main usa-layout-docs grid-col-12 pmc-layout pmc-prose padding-0" > <section class="pmc-journal-banner text-center line-height-none" aria-label="Journal banner"><img src="https://cdn.ncbi.nlm.nih.gov/pmc/banners/logo-plosone.png" alt="PLOS ONE logo" usemap="#pmc-banner-imagemap" width="500" height="75"><map name="pmc-banner-imagemap"><area alt="Link to PLOS ONE" title="Link to PLOS ONE" shape="default" href="https://journals.plos.org/plosone/" target="_blank" rel="noopener noreferrer"></map></section><article lang="en"><section aria-label="Article citation and metadata"><section class="pmc-layout__citation font-secondary font-xs"><div> <div class="display-inline-block"><button type="button" class="cursor-pointer text-no-underline bg-transparent border-0 padding-0 text-left margin-0 text-normal text-primary" aria-controls="journal_context_menu">PLoS One</button></div>. 2012 Mar 14;7(3):e31781. doi: <a href="https://doi.org/10.1371/journal.pone.0031781" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">10.1371/journal.pone.0031781</a> </div> <nav id="journal_context_menu" hidden="hidden"><ul class="menu-list font-family-ui" role="menu"> <li role="presentation"><a href="https://www.ncbi.nlm.nih.gov/pmc/?term=%22PLoS%20One%22%5Bjour%5D" class="usa-link" role="menuitem">Search in PMC</a></li> <li role="presentation"><a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22PLoS%20One%22%5Bjour%5D" lang="en" class="usa-link" role="menuitem">Search in PubMed</a></li> <li role="presentation"><a href="https://www.ncbi.nlm.nih.gov/nlmcatalog?term=%22PLoS%20One%22%5BTitle%20Abbreviation%5D" class="usa-link" role="menuitem">View in NLM Catalog</a></li> <li role="presentation"><a href="?term=%22PLoS%20One%22%5Bjour%5D" class="usa-link" role="menuitem" data-add-to-search="true">Add to search</a></li> </ul></nav></section><section class="front-matter"><div class="ameta p font-secondary font-xs"> <hgroup><h1>Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation</h1></hgroup><div class="cg p"> <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Erickson%20GM%22%5BAuthor%5D" class="usa-link" aria-describedby="id1"><span class="name western">Gregory M Erickson</span></a><div hidden="hidden" id="id1"> <h3><span class="name western">Gregory M Erickson</span></h3> <div class="p"> <sup>1</sup>Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Erickson%20GM%22%5BAuthor%5D" class="usa-link"><span class="name western">Gregory M Erickson</span></a> </div> </div> <sup>1,</sup><sup>*</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Gignac%20PM%22%5BAuthor%5D" class="usa-link" aria-describedby="id2"><span class="name western">Paul M Gignac</span></a><div hidden="hidden" id="id2"> <h3><span class="name western">Paul M Gignac</span></h3> <div class="p"> <sup>1</sup>Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Gignac%20PM%22%5BAuthor%5D" class="usa-link"><span class="name western">Paul M Gignac</span></a> </div> </div> <sup>1,</sup><sup>¤</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Steppan%20SJ%22%5BAuthor%5D" class="usa-link" aria-describedby="id3"><span class="name western">Scott J Steppan</span></a><div hidden="hidden" id="id3"> <h3><span class="name western">Scott J Steppan</span></h3> <div class="p"> <sup>1</sup>Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Steppan%20SJ%22%5BAuthor%5D" class="usa-link"><span class="name western">Scott J Steppan</span></a> </div> </div> <sup>1</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Lappin%20AK%22%5BAuthor%5D" class="usa-link" aria-describedby="id4"><span class="name western">A Kristopher Lappin</span></a><div hidden="hidden" id="id4"> <h3><span class="name western">A Kristopher Lappin</span></h3> <div class="p"> <sup>2</sup>Biological Sciences Department, California State Polytechnic University, Pomona, California, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Lappin%20AK%22%5BAuthor%5D" class="usa-link"><span class="name western">A Kristopher Lappin</span></a> </div> </div> <sup>2</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Vliet%20KA%22%5BAuthor%5D" class="usa-link" aria-describedby="id5"><span class="name western">Kent A Vliet</span></a><div hidden="hidden" id="id5"> <h3><span class="name western">Kent A Vliet</span></h3> <div class="p"> <sup>3</sup>Department of Biology, University of Florida, Gainesville, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Vliet%20KA%22%5BAuthor%5D" class="usa-link"><span class="name western">Kent A Vliet</span></a> </div> </div> <sup>3</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Brueggen%20JD%22%5BAuthor%5D" class="usa-link" aria-describedby="id6"><span class="name western">John D Brueggen</span></a><div hidden="hidden" id="id6"> <h3><span class="name western">John D Brueggen</span></h3> <div class="p"> <sup>4</sup>St. Augustine Alligator Farm Zoological Park, St. Augustine, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Brueggen%20JD%22%5BAuthor%5D" class="usa-link"><span class="name western">John D Brueggen</span></a> </div> </div> <sup>4</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Inouye%20BD%22%5BAuthor%5D" class="usa-link" aria-describedby="id7"><span class="name western">Brian D Inouye</span></a><div hidden="hidden" id="id7"> <h3><span class="name western">Brian D Inouye</span></h3> <div class="p"> <sup>1</sup>Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Inouye%20BD%22%5BAuthor%5D" class="usa-link"><span class="name western">Brian D Inouye</span></a> </div> </div> <sup>1</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Kledzik%20D%22%5BAuthor%5D" class="usa-link" aria-describedby="id8"><span class="name western">David Kledzik</span></a><div hidden="hidden" id="id8"> <h3><span class="name western">David Kledzik</span></h3> <div class="p"> <sup>4</sup>St. Augustine Alligator Farm Zoological Park, St. Augustine, Florida, United States of America</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Kledzik%20D%22%5BAuthor%5D" class="usa-link"><span class="name western">David Kledzik</span></a> </div> </div> <sup>4</sup>, <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Webb%20GJW%22%5BAuthor%5D" class="usa-link" aria-describedby="id9"><span class="name western">Grahame J W Webb</span></a><div hidden="hidden" id="id9"> <h3><span class="name western">Grahame J W Webb</span></h3> <div class="p"> <sup>5</sup>Wildlife Management International, Karama, and School of Environmental Research, Charles Darwin University, Darwin, Northern Territories, Australia</div> <div class="p">Find articles by <a href="https://pubmed.ncbi.nlm.nih.gov/?term=%22Webb%20GJW%22%5BAuthor%5D" class="usa-link"><span class="name western">Grahame J W Webb</span></a> </div> </div> <sup>5</sup> </div> <div class="cg p">Editor: <span class="name western">Leon Claessens</span><sup>6</sup> </div> <ul class="d-buttons inline-list"> <li><button class="d-button" aria-controls="aip_a" aria-expanded="false">Author information</button></li> <li><button class="d-button" aria-controls="anp_a" aria-expanded="false">Article notes</button></li> <li><button class="d-button" aria-controls="clp_a" aria-expanded="false">Copyright and License information</button></li> </ul> <div class="d-panels font-secondary-light"> <div id="aip_a" class="d-panel p" style="display: none"> <div class="p" id="aff1"> <sup>1</sup>Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America</div> <div id="aff2"> <sup>2</sup>Biological Sciences Department, California State Polytechnic University, Pomona, California, United States of America</div> <div id="aff3"> <sup>3</sup>Department of Biology, University of Florida, Gainesville, Florida, United States of America</div> <div id="aff4"> <sup>4</sup>St. Augustine Alligator Farm Zoological Park, St. Augustine, Florida, United States of America</div> <div id="aff5"> <sup>5</sup>Wildlife Management International, Karama, and School of Environmental Research, Charles Darwin University, Darwin, Northern Territories, Australia</div> <div id="edit1"> <sup>6</sup>College of the Holy Cross, United States of America</div> <div class="author-notes p"> <div class="fn" id="cor1"> <sup>✉</sup><p class="display-inline">* E-mail: <span>gerickson@bio.fsu.edu</span></p> </div> <div class="fn" id="fn1_pmc"><p>Conceived and designed the experiments: GME PMG AKL KAV. Performed the experiments: GME PMG AKL KAV JDB DK GJWW. Analyzed the data: GME PMG SJS AKL BDI. Contributed reagents/materials/analysis tools: GME SJS JDB BDI GJWW. Wrote the paper: GME PMG SJS AKL BDI GJWW.</p></div> <div class="fn" id="fn1"> <sup>¤</sup><p class="display-inline">Current address: Department of Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, New York, United States of America</p> </div> </div> <h4 class="font-secondary">Roles</h4> <div class="p"> <strong class="contrib"><span class="name western">Leon Claessens</span></strong>: <span class="role">Editor</span> </div> </div> <div id="anp_a" class="d-panel p" style="display: none"><div class="notes p"><section id="historyarticle-meta1" class="history"><p>Received 2011 Feb 22; Accepted 2012 Jan 19; Collection date 2012.</p></section></div></div> <div id="clp_a" class="d-panel p" style="display: none"> <div>Erickson et al.</div> <p>This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.</p> <div class="p"><a href="/about/copyright/" class="usa-link">PMC Copyright notice</a></div> </div> </div> <div>PMCID: PMC3303775 PMID: <a href="https://pubmed.ncbi.nlm.nih.gov/22431965/" class="usa-link">22431965</a> </div> </div></section></section><section aria-label="Article content"><section class="body main-article-body"><section class="abstract" id="abstract1"><h2>Abstract</h2> <section id="sec1"><h3 class="pmc_sec_title">Background</h3> <p>Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known.</p></section><section id="sec2"><h3 class="pmc_sec_title">Methodology/Principal Findings</h3> <p>We measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research.</p></section><section id="sec3"><h3 class="pmc_sec_title">Conclusions/Significance</h3> <p>Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.</p></section></section><section id="s1"><h2 class="pmc_sec_title">Introduction</h2> <p>Despite their large size (1.2–6.7 m total length <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>), crocodilians (Crocodylia: Alligatoridae: [alligators and caimans]; Crocodylidae: [crocodiles]; Gavialidae: [Indian and Malay (“false”) gharials]; <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a>, <a href="#pone.0031781-Brochu1" class="usa-link" aria-describedby="pone.0031781-Brochu1">[3]</a>) are remarkably stealthy predators – adept at stalking and ambushing prey in and around freshwater and estuarine environments. For the most part, their post-cranial anatomy related to locomotion is similar between species <a href="#pone.0031781-Frey1" class="usa-link" aria-describedby="pone.0031781-Frey1">[4]</a>, <a href="#pone.0031781-Parrish1" class="usa-link" aria-describedby="pone.0031781-Parrish1">[5]</a>. Conversely adult body sizes and cranio-dental anatomy are conspicuously variable <a href="#pone.0031781-Brochu1" class="usa-link" aria-describedby="pone.0031781-Brochu1">[3]</a>, <a href="#pone.0031781-Brochu2" class="usa-link" aria-describedby="pone.0031781-Brochu2">[6]</a> (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>). Adults of all species are opportunistic feeders with diets that can include invertebrates, fish, snakes, turtles, birds and mammals <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, <a href="#pone.0031781-Pooley1" class="usa-link" aria-describedby="pone.0031781-Pooley1">[7]</a>. This is especially true of dietary generalists with teeth and snouts that occupy the middle ground among crocodilians with regard to sharpness and width, respectively. These include taxa such as the saltwater crocodile (<em>Crocodylus porosus</em>) and American alligator (<em>Alligator mississippiensis</em>) (<a href="#pone-0031781-g001" class="usa-link">Figures 1</a> and <a href="#pone-0031781-g002" class="usa-link">2</a>). On the other hand, those with extreme rostro-dental morphology tend to have more specialized diets. Several extremely slender-snouted forms with needle-like teeth, such as the Australian freshwater crocodile (<em>Crocodylus johnsoni</em>) and the Indian gharial (<em>Gavialis gangeticus</em>), consume a preponderance of small compliant prey such as fish, insects, and crustaceans <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, <a href="#pone.0031781-Pooley1" class="usa-link" aria-describedby="pone.0031781-Pooley1">[7]</a>, <a href="#pone.0031781-Thorbjarnarson1" class="usa-link" aria-describedby="pone.0031781-Thorbjarnarson1">[8]</a> (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>). Their elongated jaws, although structurally weak in bending <a href="#pone.0031781-Busbey1" class="usa-link" aria-describedby="pone.0031781-Busbey1">[9]</a>–<a href="#pone.0031781-Pierce1" class="usa-link" aria-describedby="pone.0031781-Pierce1">[11]</a>, afford a broad strike zone during side-to-side head motions, rapid distal jaw closure, and we suspect, less obstructed vision when targeting prey. The broad-snouted caiman (<em>Caiman latirostris</em>) and Chinese alligator (<em>Alligator sinensis</em>) have blunt rostra and dull bulbous teeth for consuming hard-shelled mollusks <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, <a href="#pone.0031781-Pooley1" class="usa-link" aria-describedby="pone.0031781-Pooley1">[7]</a>, <a href="#pone.0031781-Borteiro1" class="usa-link" aria-describedby="pone.0031781-Borteiro1">[12]</a> (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>). This rostro-dental morphology helps to ensure enhanced structural rigidity through lower bending moments <a href="#pone.0031781-Busbey1" class="usa-link" aria-describedby="pone.0031781-Busbey1">[9]</a>. Additionally, high bite forces occur at all tooth positions due to their proximity to the jaw joint <a href="#pone.0031781-Busbey1" class="usa-link" aria-describedby="pone.0031781-Busbey1">[9]</a>–<a href="#pone.0031781-Pierce1" class="usa-link" aria-describedby="pone.0031781-Pierce1">[11]</a>. Finally, the dwarf caimans (<em>Paleosuchus trigonatus</em> and <em>Paleosuchus palpebrosus</em>) have dog-like vaulted rostra, and teeth with intermediate sharpness (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>). Both feed at the water's edge; <em>Paleosuchus trigonatus</em> also forages on land for snakes, pacas and porcupines <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, <a href="#pone.0031781-Pooley1" class="usa-link" aria-describedby="pone.0031781-Pooley1">[7]</a>, <a href="#pone.0031781-Magnusson1" class="usa-link" aria-describedby="pone.0031781-Magnusson1">[13]</a>. Their dorso-ventrally expanded snouts enhance rigidity in the plane of biting through increased area moments of inertia <a href="#pone.0031781-Busbey1" class="usa-link" aria-describedby="pone.0031781-Busbey1">[9]</a>, <a href="#pone.0031781-McHenry1" class="usa-link" aria-describedby="pone.0031781-McHenry1">[10]</a>.</p> <figure class="fig xbox font-sm" id="pone-0031781-g001"><h3 class="obj_head">Figure 1. Phylogenetic hypothesis for extant Crocodylia showing variation in rostral proportions.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g001.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/fb5dcd7822b1/pone.0031781.g001.jpg" loading="lazy" height="577" width="430" alt="Figure 1"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g001/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>The cladogram is based on reanalysis (see <a href="#s4" class="usa-link">Materials and Methods</a>) of molecular data from Gatesy and colleagues <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a> using maximum likelihood and non-parametric rate-smoothing with branch lengths proportional to time. Lineages shown in blue represent caiman (a–e) and alligators (f,g) ( = Alligatoridae), and those in green crocodiles (h–t) and gharials (u,v) ( = Crocodylidae+Gavialidae). The Yacare caiman, <em>Caiman yacare</em> is not shown for it was not utilized in the Gatesy et al. <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a> analysis. Dorsal views of heads are modified from Wermuth and Fuchs <a href="#pone.0031781-Wermuth1" class="usa-link" aria-describedby="pone.0031781-Wermuth1">[53]</a> and standardized to the same length to show relative differences in rostral form. Bracketed numbers following taxon names are the mean rostral proportions or RP ( = mid-rostral width/snout length) for each taxon from our study. Phylogenetic Independent Contrasts were performed on these 22 species; however, bite force, tooth pressure, and morphometric measurements and subsequent TIPs analyses were performed for all 23 extant taxa, including <em>Caiman yacare</em>.</p></figcaption></figure><figure class="fig xbox font-sm" id="pone-0031781-g002"><h3 class="obj_head">Figure 2. Skull and jaws of a wild adult American alligator (<em>Alligator mississippiensis</em>) showing the prominent teeth used for initially seizing and crushing prey.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g002.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/2531170fd32c/pone.0031781.g002.jpg" loading="lazy" height="187" width="430" alt="Figure 2"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g002/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>The most prominent caniniform and molariform teeth of the upper jaw that are associated with the convexities in the maxilla are highlighted. Because of their greater length relative to the adjacent teeth, and the propensity of crocodilians to bite unilaterally, the crowns of these teeth typically initiate contact with prey during biting. This specimen demonstrates the natural <em>in situ</em> condition of the teeth, which often fall out during skeletonization and must be reattached. As such the natural prominence of the teeth is sometimes not represented in prepared specimens. The caniniform teeth in crocodilians are longer, more slender, and generally have rounder cross-sectional shapes than the molariform teeth. In <em>A. mississippiensis</em> the apices of the caniniforms are fairly dull, whereas in more piscivorous species they are sharp and needle-like. Besides being utilized for seizing prey, caniniform teeth are also used in fighting, defense, aggression, and display. Crocodilian molariforms, on the other hand, are shorter and are typically blunter-tipped than the caniniform teeth. They range interspecifically from having a rounded bulbous morphology to being laterally compressed and blade-like. The intermediate condition seen here is characteristic of <em>A. mississippiensis</em>. Molariform teeth are primarily used for crushing and gripping prey in preparation for swallowing, but are also utilized for display and seizing prey.</p></figcaption></figure><p>The biomechanics of crocodilian feeding is poorly understood. Most notably it is not known how crocodilian bite forces and tooth pressures (bite force/tooth contact area) relate to rostro-dental and body size variance, dietary ecology, or evolutionary diversifications. Adult bite forces are only known for <em>Alligator mississippiensis</em> <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a>, but are assumed to vary considerably among taxa. This is because of marked differences in the robustness of crocodilian teeth and jaws, dietary constituency (e.g. hard versus compliant prey <a href="#pone.0031781-Neill1" class="usa-link" aria-describedby="pone.0031781-Neill1">[16]</a>), and perhaps myology <a href="#pone.0031781-Iordansky1" class="usa-link" aria-describedby="pone.0031781-Iordansky1">[17]</a>–<a href="#pone.0031781-Endo1" class="usa-link" aria-describedby="pone.0031781-Endo1">[19]</a>. Recent computerized finite element modeling of crocodilian skulls supports this hypothesis <a href="#pone.0031781-McHenry1" class="usa-link" aria-describedby="pone.0031781-McHenry1">[10]</a> <a href="#pone.0031781-Pierce1" class="usa-link" aria-describedby="pone.0031781-Pierce1">[11]</a>. Bite forces are predicted to vary nine-fold among animals scaled to the same head size. Extremely low forces are posited in the delicate, slender-snouted forms and highest values in the robust, blunt-snouted taxa. The concurrent effects of interspecific differences in body size on bite force have not been explored, nor have the effects of phylogeny. Likewise, to our knowledge, tooth pressures (which reflect how such forces are actually transmitted to the prey) have not been studied in reptiles. (They are however known or estimated for humans, and a few animals such as sharks and other fish <a href="#pone.0031781-Snodgrass1" class="usa-link" aria-describedby="pone.0031781-Snodgrass1">[20]</a>–<a href="#pone.0031781-Anderson1" class="usa-link" aria-describedby="pone.0031781-Anderson1">[22]</a>.)</p> <p>Here we formally tested the longstanding hypothesis that crocodilian rostal proportions positively correlate with the capacity for bite-force generation. In addition, owing to the lack of speculation on how absolute bite forces and tooth pressures differ among extant crocodilians, we tested the hypothesis that these values scale isometrically with body mass.</p> <p>We directly measured bite forces in sexually mature adults of all 23 extant crocodilian species <a href="#pone.0031781-King1" class="usa-link" aria-describedby="pone.0031781-King1">[23]</a> (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>) and inferred their peak tooth pressures at the prominent upper caniniform teeth (at the maxilla convexity near the front of the jaws) where prey are initially seized, and at the prominent upper molariform teeth (at the maxilla convexity nearer the back of the jaws) where food items are orally processed (<a href="#pone-0031781-g002" class="usa-link">Figure 2</a>; also see <a href="#s4" class="usa-link">Materials and Methods</a>). We then tested the extent to which variation in forces and pressures could be explained by body size and rostral type. Spurious correlations were avoided by examining the effects of phylogenic relationships using independent contrasts. Finally, the biomechanical-performance traits were mapped onto a highly robust, re-estimated DNA sequence phylogeny to visualize character evolution and make evolutionary inferences about the role feeding biomechanics played in crocodilian ecological diversifications (see <a href="#s4" class="usa-link">Materials and Methods</a>).</p> <section class="tw xbox font-sm" id="pone-0031781-t001"><h3 class="obj_head">Table 1. Anatomical measurements, and bite-force performance for extant Crocodylia.</h3> <div class="tbl-box p" tabindex="0"><table class="content" frame="hsides" rules="groups"> <colgroup span="1"> <col align="left" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> </colgroup> <thead><tr> <td align="left" rowspan="1" colspan="1">Taxon</td> <td align="left" rowspan="1" colspan="1">N</td> <td align="left" rowspan="1" colspan="1">MRP</td> <td align="left" rowspan="1" colspan="1">MBM</td> <td align="left" rowspan="1" colspan="1">RBM</td> <td align="left" rowspan="1" colspan="1">MTL</td> <td align="left" rowspan="1" colspan="1">RTL</td> <td align="left" rowspan="1" colspan="1">MBF</td> <td align="left" rowspan="1" colspan="1">RMBF</td> <td align="left" rowspan="1" colspan="1">MTFR</td> <td align="left" rowspan="1" colspan="1">CBF</td> <td align="left" rowspan="1" colspan="1">RCBF</td> </tr></thead> <tbody> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Crocodylidae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus acutus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">0.40</td> <td align="left" rowspan="1" colspan="1">132</td> <td align="left" rowspan="1" colspan="1">100–164</td> <td align="left" rowspan="1" colspan="1">294</td> <td align="left" rowspan="1" colspan="1">270–318</td> <td align="left" rowspan="1" colspan="1">3999</td> <td align="left" rowspan="1" colspan="1">3643–4355</td> <td align="left" rowspan="1" colspan="1">1.54</td> <td align="left" rowspan="1" colspan="1">2599</td> <td align="left" rowspan="1" colspan="1">2368–2830</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus intermedius</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">0.35</td> <td align="left" rowspan="1" colspan="1">182</td> <td align="left" rowspan="1" colspan="1">182</td> <td align="left" rowspan="1" colspan="1">340</td> <td align="left" rowspan="1" colspan="1">340</td> <td align="left" rowspan="1" colspan="1">6276</td> <td align="left" rowspan="1" colspan="1">6276</td> <td align="left" rowspan="1" colspan="1">1.59</td> <td align="left" rowspan="1" colspan="1">4283</td> <td align="left" rowspan="1" colspan="1">4283</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus johnsoni</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">0.24</td> <td align="left" rowspan="1" colspan="1">20</td> <td align="left" rowspan="1" colspan="1">7–43</td> <td align="left" rowspan="1" colspan="1">167</td> <td align="left" rowspan="1" colspan="1">134–215</td> <td align="left" rowspan="1" colspan="1">1292</td> <td align="left" rowspan="1" colspan="1">859–1863</td> <td align="left" rowspan="1" colspan="1">2.05</td> <td align="left" rowspan="1" colspan="1">629</td> <td align="left" rowspan="1" colspan="1">418–856</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus mindorensis</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">0.65</td> <td align="left" rowspan="1" colspan="1">69</td> <td align="left" rowspan="1" colspan="1">69</td> <td align="left" rowspan="1" colspan="1">244</td> <td align="left" rowspan="1" colspan="1">244</td> <td align="left" rowspan="1" colspan="1">2736</td> <td align="left" rowspan="1" colspan="1">2736</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus moreletii</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">0.75</td> <td align="left" rowspan="1" colspan="1">110</td> <td align="left" rowspan="1" colspan="1">110</td> <td align="left" rowspan="1" colspan="1">284</td> <td align="left" rowspan="1" colspan="1">284</td> <td align="left" rowspan="1" colspan="1">4399</td> <td align="left" rowspan="1" colspan="1">4399</td> <td align="left" rowspan="1" colspan="1">1.43</td> <td align="left" rowspan="1" colspan="1">3069</td> <td align="left" rowspan="1" colspan="1">3069</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus niloticus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">0.47</td> <td align="left" rowspan="1" colspan="1">86</td> <td align="left" rowspan="1" colspan="1">86–87</td> <td align="left" rowspan="1" colspan="1">250</td> <td align="left" rowspan="1" colspan="1">240–261</td> <td align="left" rowspan="1" colspan="1">3043</td> <td align="left" rowspan="1" colspan="1">2914–3172</td> <td align="left" rowspan="1" colspan="1">1.51</td> <td align="left" rowspan="1" colspan="1">2007</td> <td align="left" rowspan="1" colspan="1">1991–2023</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus novaeguineae</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">0.55</td> <td align="left" rowspan="1" colspan="1">154</td> <td align="left" rowspan="1" colspan="1">123–186</td> <td align="left" rowspan="1" colspan="1">303</td> <td align="left" rowspan="1" colspan="1">291–315</td> <td align="left" rowspan="1" colspan="1">5360</td> <td align="left" rowspan="1" colspan="1">4782–5938</td> <td align="left" rowspan="1" colspan="1">1.36</td> <td align="left" rowspan="1" colspan="1">3928</td> <td align="left" rowspan="1" colspan="1">3547–4310</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus palustris</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">0.66</td> <td align="left" rowspan="1" colspan="1">207</td> <td align="left" rowspan="1" colspan="1">207</td> <td align="left" rowspan="1" colspan="1">332</td> <td align="left" rowspan="1" colspan="1">332</td> <td align="left" rowspan="1" colspan="1">7295</td> <td align="left" rowspan="1" colspan="1">7295</td> <td align="left" rowspan="1" colspan="1">1.74</td> <td align="left" rowspan="1" colspan="1">4194</td> <td align="left" rowspan="1" colspan="1">4194</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus porosus</em> </td> <td align="left" rowspan="1" colspan="1">7</td> <td align="left" rowspan="1" colspan="1">0.41</td> <td align="left" rowspan="1" colspan="1">272</td> <td align="left" rowspan="1" colspan="1">36–531</td> <td align="left" rowspan="1" colspan="1">344</td> <td align="left" rowspan="1" colspan="1">202–459</td> <td align="left" rowspan="1" colspan="1">8983</td> <td align="left" rowspan="1" colspan="1">1446–16414</td> <td align="left" rowspan="1" colspan="1">1.57</td> <td align="left" rowspan="1" colspan="1">5792</td> <td align="left" rowspan="1" colspan="1">930–11216</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus rhombifer</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.51</td> <td align="left" rowspan="1" colspan="1">52</td> <td align="left" rowspan="1" colspan="1">30–65</td> <td align="left" rowspan="1" colspan="1">214</td> <td align="left" rowspan="1" colspan="1">187–246</td> <td align="left" rowspan="1" colspan="1">2107</td> <td align="left" rowspan="1" colspan="1">1392–3127</td> <td align="left" rowspan="1" colspan="1">1.52</td> <td align="left" rowspan="1" colspan="1">1379</td> <td align="left" rowspan="1" colspan="1">917–2035</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus siamensis</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.64</td> <td align="left" rowspan="1" colspan="1">69</td> <td align="left" rowspan="1" colspan="1">40–87</td> <td align="left" rowspan="1" colspan="1">238</td> <td align="left" rowspan="1" colspan="1">212–263</td> <td align="left" rowspan="1" colspan="1">3415</td> <td align="left" rowspan="1" colspan="1">2073–4577</td> <td align="left" rowspan="1" colspan="1">1.53</td> <td align="left" rowspan="1" colspan="1">2227</td> <td align="left" rowspan="1" colspan="1">1357–2891</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Mecistops cataphractus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.25</td> <td align="left" rowspan="1" colspan="1">67</td> <td align="left" rowspan="1" colspan="1">50–95</td> <td align="left" rowspan="1" colspan="1">247</td> <td align="left" rowspan="1" colspan="1">231–262</td> <td align="left" rowspan="1" colspan="1">2082</td> <td align="left" rowspan="1" colspan="1">1704–2447</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Osteolaemus tetraspis</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">0.66</td> <td align="left" rowspan="1" colspan="1">17</td> <td align="left" rowspan="1" colspan="1">9–34</td> <td align="left" rowspan="1" colspan="1">147</td> <td align="left" rowspan="1" colspan="1">124–183</td> <td align="left" rowspan="1" colspan="1">1787</td> <td align="left" rowspan="1" colspan="1">1375–2509</td> <td align="left" rowspan="1" colspan="1">1.53</td> <td align="left" rowspan="1" colspan="1">1164</td> <td align="left" rowspan="1" colspan="1">902–1588</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Gavialidae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Gavialis gangeticus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">0.10</td> <td align="left" rowspan="1" colspan="1">112</td> <td align="left" rowspan="1" colspan="1">103–121</td> <td align="left" rowspan="1" colspan="1">326</td> <td align="left" rowspan="1" colspan="1">318–334</td> <td align="left" rowspan="1" colspan="1">1895</td> <td align="left" rowspan="1" colspan="1">1784–2006</td> <td align="left" rowspan="1" colspan="1">2.06</td> <td align="left" rowspan="1" colspan="1">924</td> <td align="left" rowspan="1" colspan="1">819–1030</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Tomistoma schlegelii</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.18</td> <td align="left" rowspan="1" colspan="1">142</td> <td align="left" rowspan="1" colspan="1">79–255</td> <td align="left" rowspan="1" colspan="1">347</td> <td align="left" rowspan="1" colspan="1">290–405</td> <td align="left" rowspan="1" colspan="1">3397</td> <td align="left" rowspan="1" colspan="1">1704–6450</td> <td align="left" rowspan="1" colspan="1">1.62</td> <td align="left" rowspan="1" colspan="1">2099</td> <td align="left" rowspan="1" colspan="1">1052–3985</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Alligatoridae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Alligator mississippiensis</em> </td> <td align="left" rowspan="1" colspan="1">15</td> <td align="left" rowspan="1" colspan="1">0.69</td> <td align="left" rowspan="1" colspan="1">142</td> <td align="left" rowspan="1" colspan="1">47–297</td> <td align="left" rowspan="1" colspan="1">285</td> <td align="left" rowspan="1" colspan="1">213–372</td> <td align="left" rowspan="1" colspan="1">5117</td> <td align="left" rowspan="1" colspan="1">2442–9452</td> <td align="left" rowspan="1" colspan="1">1.54</td> <td align="left" rowspan="1" colspan="1">3340</td> <td align="left" rowspan="1" colspan="1">1414–6162</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Alligator sinensis</em> </td> <td align="left" rowspan="1" colspan="1">4</td> <td align="left" rowspan="1" colspan="1">0.83</td> <td align="left" rowspan="1" colspan="1">14</td> <td align="left" rowspan="1" colspan="1">12–15</td> <td align="left" rowspan="1" colspan="1">150</td> <td align="left" rowspan="1" colspan="1">140–155</td> <td align="left" rowspan="1" colspan="1">1084</td> <td align="left" rowspan="1" colspan="1">894–1357</td> <td align="left" rowspan="1" colspan="1">1.48</td> <td align="left" rowspan="1" colspan="1">735</td> <td align="left" rowspan="1" colspan="1">555–963</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman crocodilus</em> </td> <td align="left" rowspan="1" colspan="1">4</td> <td align="left" rowspan="1" colspan="1">0.58</td> <td align="left" rowspan="1" colspan="1">20</td> <td align="left" rowspan="1" colspan="1">18–25</td> <td align="left" rowspan="1" colspan="1">166</td> <td align="left" rowspan="1" colspan="1">166</td> <td align="left" rowspan="1" colspan="1">1215</td> <td align="left" rowspan="1" colspan="1">1148–1303</td> <td align="left" rowspan="1" colspan="1">1.48</td> <td align="left" rowspan="1" colspan="1">821</td> <td align="left" rowspan="1" colspan="1">759–894</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman latirostris</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">0.89</td> <td align="left" rowspan="1" colspan="1">30</td> <td align="left" rowspan="1" colspan="1">16–45</td> <td align="left" rowspan="1" colspan="1">167</td> <td align="left" rowspan="1" colspan="1">157–177</td> <td align="left" rowspan="1" colspan="1">1467</td> <td align="left" rowspan="1" colspan="1">1050–2420</td> <td align="left" rowspan="1" colspan="1">1.37</td> <td align="left" rowspan="1" colspan="1">1063</td> <td align="left" rowspan="1" colspan="1">777–1672</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman yacare</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">0.69</td> <td align="left" rowspan="1" colspan="1">18</td> <td align="left" rowspan="1" colspan="1">17–23</td> <td align="left" rowspan="1" colspan="1">162</td> <td align="left" rowspan="1" colspan="1">162</td> <td align="left" rowspan="1" colspan="1">971</td> <td align="left" rowspan="1" colspan="1">712–1192</td> <td align="left" rowspan="1" colspan="1">1.50</td> <td align="left" rowspan="1" colspan="1">646</td> <td align="left" rowspan="1" colspan="1">485–900</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Melanosuchus niger</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.73</td> <td align="left" rowspan="1" colspan="1">59</td> <td align="left" rowspan="1" colspan="1">31–103</td> <td align="left" rowspan="1" colspan="1">246</td> <td align="left" rowspan="1" colspan="1">304</td> <td align="left" rowspan="1" colspan="1">2696</td> <td align="left" rowspan="1" colspan="1">1779–4310</td> <td align="left" rowspan="1" colspan="1">1.42</td> <td align="left" rowspan="1" colspan="1">1911</td> <td align="left" rowspan="1" colspan="1">1180–3112</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Paleosuchus palpebrosus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.69</td> <td align="left" rowspan="1" colspan="1">13</td> <td align="left" rowspan="1" colspan="1">12–14</td> <td align="left" rowspan="1" colspan="1">133</td> <td align="left" rowspan="1" colspan="1">133</td> <td align="left" rowspan="1" colspan="1">900</td> <td align="left" rowspan="1" colspan="1">667–1125</td> <td align="left" rowspan="1" colspan="1">1.56</td> <td align="left" rowspan="1" colspan="1">576</td> <td align="left" rowspan="1" colspan="1">436–711</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Paleosuchus trigonatus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">0.51</td> <td align="left" rowspan="1" colspan="1">22</td> <td align="left" rowspan="1" colspan="1">19–28</td> <td align="left" rowspan="1" colspan="1">150</td> <td align="left" rowspan="1" colspan="1">143–156</td> <td align="left" rowspan="1" colspan="1">1082</td> <td align="left" rowspan="1" colspan="1">1058–1125</td> <td align="left" rowspan="1" colspan="1">1.59</td> <td align="left" rowspan="1" colspan="1">682</td> <td align="left" rowspan="1" colspan="1">658–720</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Total</strong> </td> <td align="left" rowspan="1" colspan="1"> <strong>83</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>7–531</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>124–459</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>667–16414</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>436–11216</strong> </td> </tr> </tbody> </table></div> <div class="p text-right font-secondary"><a href="table/pone-0031781-t001/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <div class="tw-foot p"> <div class="fn" id="nt101"><p> <strong>N</strong> = Number of Specimens.</p></div> <div class="fn" id="nt102"><p> <strong>MRP</strong> = Mean Rostral Proportion (mid-rostral width/snout length).</p></div> <div class="fn" id="nt103"><p> <strong>MBM</strong> = Mean Body Mass (kg).</p></div> <div class="fn" id="nt104"><p> <strong>RBM</strong> = Range of Body Masses (kg).</p></div> <div class="fn" id="nt105"><p> <strong>MTL</strong> = Mean Total Length (cm).</p></div> <div class="fn" id="nt106"><p> <strong>RTL</strong> = Range of Total lengths (cm).</p></div> <div class="fn" id="nt107"><p> <strong>MBF</strong> = Taxon Representative Molariform Bite Force (N).</p></div> <div class="fn" id="nt108"><p> <strong>RMBF</strong> = Range of Molariform Bite Forces (N).</p></div> <div class="fn" id="nt109"><p> <strong>MTFR</strong> = Mean Tooth-Fulcrum Ratio (QA joint-Caniniform tooth/QA Joint-Molariform tooth).</p></div> <div class="fn" id="nt110"><p> <strong>CBF</strong> = Estimated Taxon Representative Caniniform Bite Force (N).</p></div> <div class="fn" id="nt111"><p> <strong>RCBF</strong> = Range of Estimated Caniniform Bite Forces (N).</p></div> </div></section></section><section id="s2"><h2 class="pmc_sec_title">Results</h2> <p>The results of our study revealed taxon representative molariform bite forces ranging from 900 to 8,983 N (202 to 2,019 lbs) (<em>Paleosuchus palpebrosus</em> and <em>Crocodylus porosus</em> respectively; <a href="#pone-0031781-t001" class="usa-link">Table 1</a>; <a href="#pone-0031781-g003" class="usa-link">Figure 3A</a>). Body mass is the primary determinant of crocodilian force generation in both the raw data analysis (TIPs: R<sup>2</sup> = 0.92) and phylogenetically corrected analysis (PIC: R<sup>2</sup> = 0.87, p<0.0001). The reduced major axis (RMA) scaling coefficient for log-transformed taxon representative bite force regressed against log-transformed body mass was 0.708±0.111 (95% CI), which is not statistically different from isometry (scaling coefficient = 0.667). Only the forces for <em>Gavialis gangeticus</em> in the TIPS analysis are significantly atypical (lower) than those of extant Crocodylia as a whole (<a href="#pone-0031781-g003" class="usa-link">Figure 3A</a>). Those for the Malay gharial (<em>Tomistoma schlegelii</em>) are moderately low. Interspecific differences in rostral proportions (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>; <a href="#pone-0031781-t001" class="usa-link">Table 1</a>) explain just 19% of the remaining variance in the size-standardized phylogenetically corrected data set (<a href="#pone-0031781-g003" class="usa-link">Figure 3B</a>). This represents only 2.5% of the total variance from the aforementioned phylogenetically corrected analysis. Thus, the hypothesis that crocodilian rostal proportions positively correlate with bite-force capacity, while statistically significant (p = 0.03), is not supported as a major predictor of force even after correcting for size.</p> <figure class="fig xbox font-sm" id="pone-0031781-g003"><h3 class="obj_head">Figure 3. Taxon representative adult bite forces for extant Crocodylia with respect to mean body mass and the relationship between rostral proportion and force generation.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g003.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/e1f5582e6b83/pone.0031781.g003.jpg" loading="lazy" height="235" width="661" alt="Figure 3"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g003/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>(<em>A</em>) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the strong correspondence between body mass and bite force. Extant alligators and caiman (Alligatoridae), and crocodiles (Crocodylidae) show comparable relative bite-force capacities. Note that only <em>Gavialis gangeticus</em> is a statistical (i.e. outside the 95% confidence interval) low-force outlier. (<em>B</em>) Linear regression of the size-standardized residual bite force versus rostral proportion phylogenetic independent contrasts showing the low correlation between these after accounting for phylogeny and body mass.</p></figcaption></figure><p>The taxon representative caniniform tooth-pressure values ranged from 195 to 1,344 MPa (28,282 to 194,931 psi) (Morelet's crocodile – <em>Crocodylus moreletii</em>, and the Orinoco crocodile – <em>Crocodylus intermedius</em>, respectively; <a href="#pone-0031781-t002" class="usa-link">Table 2</a>, <a href="#pone-0031781-g004" class="usa-link">Figure 4A</a>). These values also trend positively with increasing body mass, but are highly variable (TIPs: R<sup>2</sup> = 0.20; PIC: R<sup>2</sup> = 0.19, p = 0.09). The RMA scaling coefficient for log-transformed taxon representative caniniform tooth pressure regressed against log-transformed body mass was 0.490±0.203 (95% CI), which is greater (i.e. positively allometric) than isometry (scaling coefficient = 0.000), and so did not support our hypothesis. Exceptionally high values stand out in the slender-snouted, semi-piscivorous <em>Crocodylus intermedius</em>, and highly piscivorous <em>Gavialis gangeticus</em> (the latter generates the lowest relative bite force but also has exceptionally slender teeth with negligible contact area). The values for <em>Crocodylus johnsoni</em> are moderately high. All other ecomorph representatives show similar relative values. Size-standardized caniniform tooth pressures changed independently on multiple lineages (<a href="#pone-0031781-g004" class="usa-link">Figure 4B</a>) and were uncorrelated with rostral proportions (PIC R<sup>2</sup> = 0.001; <a href="#pone-0031781-g005" class="usa-link">Figure 5A</a>).</p> <section class="tw xbox font-sm" id="pone-0031781-t002"><h3 class="obj_head">Table 2. Dental measurements and pressure generation for extant Crocodylia.</h3> <div class="tbl-box p" tabindex="0"><table class="content" frame="hsides" rules="groups"> <colgroup span="1"> <col align="left" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> <col align="center" span="1"> </colgroup> <thead><tr> <td align="left" rowspan="1" colspan="1">Taxon</td> <td align="left" rowspan="1" colspan="1">N</td> <td align="left" rowspan="1" colspan="1">CCA</td> <td align="left" rowspan="1" colspan="1">RCCA</td> <td align="left" rowspan="1" colspan="1">CP</td> <td align="left" rowspan="1" colspan="1">RCP</td> <td align="left" rowspan="1" colspan="1">MCA</td> <td align="left" rowspan="1" colspan="1">RMCA</td> <td align="left" rowspan="1" colspan="1">MP</td> <td align="left" rowspan="1" colspan="1">RMP</td> </tr></thead> <tbody> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Crocodylidae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus acutus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">5.78</td> <td align="left" rowspan="1" colspan="1">5.78</td> <td align="left" rowspan="1" colspan="1">410</td> <td align="left" rowspan="1" colspan="1">410</td> <td align="left" rowspan="1" colspan="1">5.50</td> <td align="left" rowspan="1" colspan="1">4.93–6.08</td> <td align="left" rowspan="1" colspan="1">728</td> <td align="left" rowspan="1" colspan="1">716–740</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus intermedius</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">3.19</td> <td align="left" rowspan="1" colspan="1">3.19</td> <td align="left" rowspan="1" colspan="1">1344</td> <td align="left" rowspan="1" colspan="1">1344</td> <td align="left" rowspan="1" colspan="1">4.52</td> <td align="left" rowspan="1" colspan="1">4.52</td> <td align="left" rowspan="1" colspan="1">1388</td> <td align="left" rowspan="1" colspan="1">1388</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus johnsoni</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">1.01</td> <td align="left" rowspan="1" colspan="1">0.52–1.80</td> <td align="left" rowspan="1" colspan="1">624</td> <td align="left" rowspan="1" colspan="1">381–1078</td> <td align="left" rowspan="1" colspan="1">1.56</td> <td align="left" rowspan="1" colspan="1">0.51–2.14</td> <td align="left" rowspan="1" colspan="1">832</td> <td align="left" rowspan="1" colspan="1">565–1871</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus mindorensis</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">8.02</td> <td align="left" rowspan="1" colspan="1">8.02</td> <td align="left" rowspan="1" colspan="1">341</td> <td align="left" rowspan="1" colspan="1">341</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus moreletii</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">15.72</td> <td align="left" rowspan="1" colspan="1">15.72</td> <td align="left" rowspan="1" colspan="1">195</td> <td align="left" rowspan="1" colspan="1">195</td> <td align="left" rowspan="1" colspan="1">14.24</td> <td align="left" rowspan="1" colspan="1">14.24</td> <td align="left" rowspan="1" colspan="1">309</td> <td align="left" rowspan="1" colspan="1">309</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus niloticus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">6.18</td> <td align="left" rowspan="1" colspan="1">2.89–9.48</td> <td align="left" rowspan="1" colspan="1">451</td> <td align="left" rowspan="1" colspan="1">213–689</td> <td align="left" rowspan="1" colspan="1">5.41</td> <td align="left" rowspan="1" colspan="1">5.06–5.77</td> <td align="left" rowspan="1" colspan="1">566</td> <td align="left" rowspan="1" colspan="1">505–627</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus novaeguineae</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">9.30</td> <td align="left" rowspan="1" colspan="1">6.99–11.61</td> <td align="left" rowspan="1" colspan="1">439</td> <td align="left" rowspan="1" colspan="1">371–508</td> <td align="left" rowspan="1" colspan="1">5.04</td> <td align="left" rowspan="1" colspan="1">4.91–5.17</td> <td align="left" rowspan="1" colspan="1">1061</td> <td align="left" rowspan="1" colspan="1">973–1149</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus palustris</em> </td> <td align="left" rowspan="1" colspan="1">1</td> <td align="left" rowspan="1" colspan="1">10.97</td> <td align="left" rowspan="1" colspan="1">10.97</td> <td align="left" rowspan="1" colspan="1">382</td> <td align="left" rowspan="1" colspan="1">382</td> <td align="left" rowspan="1" colspan="1">14.42</td> <td align="left" rowspan="1" colspan="1">14.42</td> <td align="left" rowspan="1" colspan="1">506</td> <td align="left" rowspan="1" colspan="1">506</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus porosus</em> </td> <td align="left" rowspan="1" colspan="1">7</td> <td align="left" rowspan="1" colspan="1">8.33</td> <td align="left" rowspan="1" colspan="1">3.98–9.57</td> <td align="left" rowspan="1" colspan="1">679</td> <td align="left" rowspan="1" colspan="1">234–1343</td> <td align="left" rowspan="1" colspan="1">7.44</td> <td align="left" rowspan="1" colspan="1">2.22–16.87</td> <td align="left" rowspan="1" colspan="1">1207</td> <td align="left" rowspan="1" colspan="1">300–2473</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus rhombifer</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">4.55</td> <td align="left" rowspan="1" colspan="1">3.08–7.10</td> <td align="left" rowspan="1" colspan="1">312</td> <td align="left" rowspan="1" colspan="1">263–385</td> <td align="left" rowspan="1" colspan="1">4.48</td> <td align="left" rowspan="1" colspan="1">2.93–6.18</td> <td align="left" rowspan="1" colspan="1">466</td> <td align="left" rowspan="1" colspan="1">414–506</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Crocodylus siamensis</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">6.59</td> <td align="left" rowspan="1" colspan="1">3.32–9.85</td> <td align="left" rowspan="1" colspan="1">513</td> <td align="left" rowspan="1" colspan="1">293–732</td> <td align="left" rowspan="1" colspan="1">5.52</td> <td align="left" rowspan="1" colspan="1">4.73–6.67</td> <td align="left" rowspan="1" colspan="1">616</td> <td align="left" rowspan="1" colspan="1">402–760</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Mecistops cataphractus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">—</td> <td align="left" rowspan="1" colspan="1">4.19</td> <td align="left" rowspan="1" colspan="1">4.19</td> <td align="left" rowspan="1" colspan="1">406</td> <td align="left" rowspan="1" colspan="1">406</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Osteolaemus tetraspis</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">2.94</td> <td align="left" rowspan="1" colspan="1">1.37–5.07</td> <td align="left" rowspan="1" colspan="1">400</td> <td align="left" rowspan="1" colspan="1">241–660</td> <td align="left" rowspan="1" colspan="1">8.79</td> <td align="left" rowspan="1" colspan="1">4.73–13.91</td> <td align="left" rowspan="1" colspan="1">203</td> <td align="left" rowspan="1" colspan="1">139–343</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Gavialidae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Gavialis gangeticus</em> </td> <td align="left" rowspan="1" colspan="1">2</td> <td align="left" rowspan="1" colspan="1">0.81</td> <td align="left" rowspan="1" colspan="1">0.76–0.86</td> <td align="left" rowspan="1" colspan="1">1154</td> <td align="left" rowspan="1" colspan="1">958–1349</td> <td align="left" rowspan="1" colspan="1">2.98</td> <td align="left" rowspan="1" colspan="1">1.41–4.56</td> <td align="left" rowspan="1" colspan="1">855</td> <td align="left" rowspan="1" colspan="1">440–1270</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Tomistoma schlegelii</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">2.99</td> <td align="left" rowspan="1" colspan="1">1.72–1.84</td> <td align="left" rowspan="1" colspan="1">678</td> <td align="left" rowspan="1" colspan="1">613–737</td> <td align="left" rowspan="1" colspan="1">4.28</td> <td align="left" rowspan="1" colspan="1">3.14–5.05</td> <td align="left" rowspan="1" colspan="1">790</td> <td align="left" rowspan="1" colspan="1">337–1384</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Alligatoridae</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"></td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Alligator mississippiensis</em> </td> <td align="left" rowspan="1" colspan="1">15</td> <td align="left" rowspan="1" colspan="1">8.42</td> <td align="left" rowspan="1" colspan="1">4.16–14.67</td> <td align="left" rowspan="1" colspan="1">383</td> <td align="left" rowspan="1" colspan="1">209–722</td> <td align="left" rowspan="1" colspan="1">6.43</td> <td align="left" rowspan="1" colspan="1">4.18–8.16</td> <td align="left" rowspan="1" colspan="1">806</td> <td align="left" rowspan="1" colspan="1">299–1568</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Alligator sinensis</em> </td> <td align="left" rowspan="1" colspan="1">4</td> <td align="left" rowspan="1" colspan="1">3.60</td> <td align="left" rowspan="1" colspan="1">2.67–4.59</td> <td align="left" rowspan="1" colspan="1">207</td> <td align="left" rowspan="1" colspan="1">153–258</td> <td align="left" rowspan="1" colspan="1">5.34</td> <td align="left" rowspan="1" colspan="1">3.81–6.97</td> <td align="left" rowspan="1" colspan="1">211</td> <td align="left" rowspan="1" colspan="1">150–278</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman crocodilus</em> </td> <td align="left" rowspan="1" colspan="1">4</td> <td align="left" rowspan="1" colspan="1">3.04</td> <td align="left" rowspan="1" colspan="1">2.52–3.53</td> <td align="left" rowspan="1" colspan="1">275</td> <td align="left" rowspan="1" colspan="1">228–329</td> <td align="left" rowspan="1" colspan="1">3.58</td> <td align="left" rowspan="1" colspan="1">2.60–4.40</td> <td align="left" rowspan="1" colspan="1">351</td> <td align="left" rowspan="1" colspan="1">296–455</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman latirostris</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">3.99</td> <td align="left" rowspan="1" colspan="1">2.21–6.47</td> <td align="left" rowspan="1" colspan="1">298</td> <td align="left" rowspan="1" colspan="1">173–487</td> <td align="left" rowspan="1" colspan="1">4.18</td> <td align="left" rowspan="1" colspan="1">2.43–6.79</td> <td align="left" rowspan="1" colspan="1">372</td> <td align="left" rowspan="1" colspan="1">226–489</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Caiman yacare</em> </td> <td align="left" rowspan="1" colspan="1">5</td> <td align="left" rowspan="1" colspan="1">2.60</td> <td align="left" rowspan="1" colspan="1">1.56–4.23</td> <td align="left" rowspan="1" colspan="1">276</td> <td align="left" rowspan="1" colspan="1">164–387</td> <td align="left" rowspan="1" colspan="1">3.46</td> <td align="left" rowspan="1" colspan="1">1.76–5.92</td> <td align="left" rowspan="1" colspan="1">319</td> <td align="left" rowspan="1" colspan="1">185–515</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Melanosuchus niger</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">4.15</td> <td align="left" rowspan="1" colspan="1">3.04–5.71</td> <td align="left" rowspan="1" colspan="1">446</td> <td align="left" rowspan="1" colspan="1">320–545</td> <td align="left" rowspan="1" colspan="1">6.55</td> <td align="left" rowspan="1" colspan="1">3.92–9.22</td> <td align="left" rowspan="1" colspan="1">417</td> <td align="left" rowspan="1" colspan="1">274–509</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Paleosuchus palpebrosus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">1.58</td> <td align="left" rowspan="1" colspan="1">1.25–2.01</td> <td align="left" rowspan="1" colspan="1">365</td> <td align="left" rowspan="1" colspan="1">350–393</td> <td align="left" rowspan="1" colspan="1">2.18</td> <td align="left" rowspan="1" colspan="1">1.15–3.63</td> <td align="left" rowspan="1" colspan="1">493</td> <td align="left" rowspan="1" colspan="1">309–793</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <em>Paleosuchus trigonatus</em> </td> <td align="left" rowspan="1" colspan="1">3</td> <td align="left" rowspan="1" colspan="1">2.24</td> <td align="left" rowspan="1" colspan="1">0.88–3.08</td> <td align="left" rowspan="1" colspan="1">424</td> <td align="left" rowspan="1" colspan="1">216–815</td> <td align="left" rowspan="1" colspan="1">3.91</td> <td align="left" rowspan="1" colspan="1">3.05–4.64</td> <td align="left" rowspan="1" colspan="1">287</td> <td align="left" rowspan="1" colspan="1">228–369</td> </tr> <tr> <td align="left" rowspan="1" colspan="1"> <strong>Total</strong> </td> <td align="left" rowspan="1" colspan="1"> <strong>83</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td colspan="2" align="left" rowspan="1"> <strong>0.52–15.72</strong> </td> <td align="left" rowspan="1" colspan="1"> <strong>153–1349</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>0.51–16.87</strong> </td> <td align="left" rowspan="1" colspan="1"></td> <td align="left" rowspan="1" colspan="1"> <strong>139–2473</strong> </td> </tr> </tbody> </table></div> <div class="p text-right font-secondary"><a href="table/pone-0031781-t002/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <div class="tw-foot p"> <div class="fn" id="nt112"><p> <strong>N</strong> = Number of Specimens.</p></div> <div class="fn" id="nt113"><p> <strong>CCA</strong> = Taxon Representative Caniniform Contact Area @1 mm depth (mm<sup>2</sup>).</p></div> <div class="fn" id="nt114"><p> <strong>RCCA</strong> = Range of Caniniform Contact Areas @ 1 mm depth (mm<sup>2</sup>).</p></div> <div class="fn" id="nt115"><p> <strong>CP</strong> = Taxon Representative Caniniform Pressure (MPa).</p></div> <div class="fn" id="nt116"><p> <strong>RCP</strong> = Range of Caniniform Pressures (MPa).</p></div> <div class="fn" id="nt117"><p> <strong>MCA</strong> = Taxon Representative Molariform Contact Area @ 1 mm depth (mm<sup>2</sup>).</p></div> <div class="fn" id="nt118"><p> <strong>RMCA</strong> = Range of Molariform Contact Areas @ 1 mm depth (mm<sup>2</sup>).</p></div> <div class="fn" id="nt119"><p> <strong>MP</strong> = Taxon Representative Molariform Pressure (MPa).</p></div> <div class="fn" id="nt120"><p> <strong>RMP</strong> = Range of Molariform Pressures (MPa).</p></div> </div></section><figure class="fig xbox font-sm" id="pone-0031781-g004"><h3 class="obj_head">Figure 4. Caniniform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g004.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/e5e7a3629cd5/pone.0031781.g004.jpg" loading="lazy" height="229" width="661" alt="Figure 4"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g004/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>(<em>A</em>) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the weak relationship between body mass and caniniform pressure. Note that slender-snouted piscivorous to semi-piscivorous ecomorphs (<em>Gavialis gangeticus and Crocodylus intermedius</em>, respectively) show exceptionally high-pressure values (outside the 95% confidence interval), and <em>Crocodylus johnsoni</em> shows pressures expected of animals nearly a magnitude in size larger. Other ecomorphs show much lower and similar relative values. The arrow indicates the typical ultimate shear strength of bone. (<em>B</em>) Ancestral character-state reconstruction using squared-change parsimony of size-standardized caniniform pressures. Residual caniniform pressure values are color coded to MPa (squared-change parsimony; squared length = 19.491). Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. High relative pressures were achieved independently in <em>Crocodylus intermedius</em>, <em>Gavialis gangeticus</em>, and <em>Crocodylus johnsoni</em>. Uncolored branches represent taxa for which the caniniform teeth were shed or broken, and so pressure estimation was not possible.</p></figcaption></figure><figure class="fig xbox font-sm" id="pone-0031781-g005"><h3 class="obj_head">Figure 5. Linear regressions of residual caniniform tooth pressures, and residual molariform tooth pressures versus rostral proportion phylogenetic independent contrasts.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g005.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/76ef4062b050/pone.0031781.g005.jpg" loading="lazy" height="277" width="661" alt="Figure 5"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g005/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>The (<em>A</em>) residual caniniform, and (<em>B</em>) residual molariform regressions show the low correlation between these parameters after accounting for body mass and phylogenetic relatedness.</p></figcaption></figure><p>Taxon representative molariform tooth-pressure values ranged from 203 to 1,388 MPa (29,443 to 201,312 psi) (Dwarf crocodile – <em>Osteolaemus tetraspis</em>, and <em>Crocodylus intermedius</em>, respectively; <a href="#pone-0031781-t002" class="usa-link">Table 2</a>, <a href="#pone-0031781-g006" class="usa-link">Figure 6A</a>). These are more strongly correlated with body mass than the caniniform data (TIPs: R<sup>2</sup> = 0.54; PIC: R<sup>2</sup> = 0.293, p = 0.008). The RMA scaling coefficient for log-transformed taxon representative molariform tooth pressures regressed against log-transformed body mass was 0.553±0.180 (95% CI), which is greater (i.e. positively allometric) than isometry (scaling coefficient = 0.000), and therefore did not support our hypothesis. None of the molariform pressure values are statistical outliers. Nevertheless, those for the slender-snouted <em>Crocodylus johnsoni</em> and <em>Crocodylus intermedius</em> are relatively high, and those for the broader-snouted generalists, the mugger (<em>Crocodylus palustris</em>), and Morelet's crocodile (<em>Crocodylus moreletii</em>) are relatively low. Pressures for all other ecomorphs, including <em>Gavialis gangeticus</em>, are comparable. Size-standardized molariform tooth pressures changed repeatedly in the phylogeny (<a href="#pone-0031781-g006" class="usa-link">Figure 6B</a>) and were not significantly correlated with rostral proportions (PIC R<sup>2</sup> = 0.094; <a href="#pone-0031781-g005" class="usa-link">Figure 5B</a>).</p> <figure class="fig xbox font-sm" id="pone-0031781-g006"><h3 class="obj_head">Figure 6. Molariform pressure values for extant Crocodylia, their phylogenetic distribution, and inferred ancestral character states.</h3> <p class="img-box line-height-none margin-x-neg-2 tablet:margin-x-0 text-center"><a class="tileshop" target="_blank" href="https://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3303775_pone.0031781.g006.jpg"><img class="graphic zoom-in" src="https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e464/3303775/51f735e4493a/pone.0031781.g006.jpg" loading="lazy" height="229" width="661" alt="Figure 6"></a></p> <div class="p text-right font-secondary"><a href="figure/pone-0031781-g006/" class="usa-link" target="_blank" rel="noopener noreferrer">Open in a new tab</a></div> <figcaption><p>(<em>A</em>) Members of the Alligatoridae are shown in blue, and members of the Crocodylidae+Gavialidae in green. The OLS regression equation describes the relationship between body size and molariform pressure. Note that the range of values shows similar interspecific correspondence to the caniniform pressure data shown in <a href="#pone-0031781-g004" class="usa-link">Figure 4A</a>. The arrow indicates the typical ultimate shear strength of bone. (<em>B</em>) Ancestral-state reconstruction using squared-change parsimony of size-standardized molariform pressures. Pressures are color coded to MPa. Vertical scale is in relative time, with the outgroup/ingroup root arbitrarily set to 1.0. The notable similarities between unrelated taxa and differences between related taxa illustrate the large amount of convergence for this trait among crocodilians.</p></figcaption></figure></section><section id="s3"><h2 class="pmc_sec_title">Discussion</h2> <p>The results of our investigation into the biomechanics and evolutionary ecology of crocodilian feeding revealed a number of unexpected findings. We found negligible support for the commonly held view that bite forces correlate strongly with rostral form – a proxy for strength. Rather, bite forces vary independently of rostral morphology, so much so that in some cases same-sized taxa from the extreme bounds of crocodilian rostal morphology and dietary ecology (e.g. the slender-snouted, <em>Crocodylus johnsoni</em> and robust-snouted, <em>Caiman latirostris</em>; <a href="#pone-0031781-g001" class="usa-link">Figure 1</a>) show “pound for pound” comparable molariform bite forces (<a href="#pone-0031781-g003" class="usa-link">Figure 3A</a>). During cladogenic events, when rostral form was modified into different types (presumably to allow access to different prey), bite forces were just as likely to increase as decrease.</p> <p>Our findings suggest that for crocodilians of similar body mass, the same absolute bite forces will be generated at equal distances from the quadrate-articular joint. A consequence of this is that more slender-snouted forms will at the same time experience higher stresses to their jaws since they have lower area moments of inertia with which to resist bending. Furthermore, since they have relatively longer snouts, equal loads applied at the tip of the jaws will lead to higher absolute bending moments than in shorter-snouted forms. This begs the question: How do slender-snouted species sustain bite forces typical of more robust-snouted crocodilians? We suspect the answer lies primarily in their prey selection. They target small prey relative to their size (e.g. fish and crustaceans, and/or birds and small mammals by the larger species) whose low inertia contributes little to resistance forces. It is also plausible that their jaws experience stresses closer to rupture strength (i.e. lower safety factor <a href="#pone.0031781-Alexander1" class="usa-link" aria-describedby="pone.0031781-Alexander1">[24]</a>) during feeding than the other ecomorphs. This is certainly the case during other behaviors such as fighting and defense, where they show a much greater propensity to sustain broken jaws <a href="#pone.0031781-Huchzermeyer1" class="usa-link" aria-describedby="pone.0031781-Huchzermeyer1">[25]</a>.</p> <p>Body size actually accounts for nearly all interspecific variance in adult crocodilian bite-force capacity, and these forces scale isometrically to body mass. Clearly a major factor in the evolutionary success of crocodilians stems from their long-term retention of a cranial musculoskeletal system that can generate sufficient force to procure and process near-shore prey across a broad range of body sizes. Only in the extremely slender-snouted <em>Gavialis gangeticus</em>, arguably the only truly piscivorous species, is there evidence of significant departure in performance, and this is reflected in their anatomy. These low-force biters independently evolved extremely hypertrophied, low-mechanical advantage adductor mandibulae muscles, and small, fusiform-fibered posterior pterygoid muscles that presumably accentuate rapid jaw closure <a href="#pone.0031781-Iordansky1" class="usa-link" aria-describedby="pone.0031781-Iordansky1">[17]</a>, <a href="#pone.0031781-Endo1" class="usa-link" aria-describedby="pone.0031781-Endo1">[19]</a>. This enhanced jaw-closing performance was likely afforded at the cost of diminished bite-force capacity, which is consistent with our empirical findings for both molariform and estimated caniniform bite forces in <em>Gavialis gangeticus</em>.</p> <p>The retention of relative bite-force capacity among crocodilians makes it apparent that the remarkably high bite forces first documented in adult <em>Alligator mississippiensis</em> <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a> are typical of most comparable-sized species, regardless of rostro-dental anatomy or diet. Even higher forces are to be found in larger species like the slender-snouted, semi-piscivorous <em>Crocodylus intermedius</em> and the medium-snouted generalist <em>Crocodylus porosus</em> – the largest extant taxon. (Our datum for one <em>Crocodylus porosus</em> individual, 16,414 N [3,689 lbs] represents the highest bite force measured in any animal. This value eclipses the highest recorded value in carnivoran mammals, 4,500 N [1,011 lbs] in the spotted hyena – <em>Crocuta crocuta</em> <a href="#pone.0031781-Binder1" class="usa-link" aria-describedby="pone.0031781-Binder1">[26]</a>.)</p> <p>Crocodilian bite-force retention can be used to predict forces in other specimens and species, including taxa known only from fossils (see <a href="#s4" class="usa-link">Materials and Methods</a>). For instance, scientifically documented 6.7-meter long <em>Crocodylus porosus</em> individuals <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a> were likely capable of molariform bite forces of approximately 27,531 N to 34,424 N (6,187 to 7,736 lbs). In addition the historical range of adult bite-force values for Crocodylia as a whole may have spanned from 628 N to 102,803 N (141 to 23,102 lbs; in extinct 0.8 m TL, 1.99 kg <em>Procaimanoidea kayi</em> <a href="#pone.0031781-Mook1" class="usa-link" aria-describedby="pone.0031781-Mook1">[27]</a> and 11 m TL, 3,450 kg <em>Deinosuchus riograndensis</em> <a href="#pone.0031781-Farlow1" class="usa-link" aria-describedby="pone.0031781-Farlow1">[28]</a>, respectively; see <a href="#s4" class="usa-link">Materials and Methods</a>).</p> <p>No previous hypotheses exist regarding tooth pressures in crocodilians. Thus, the data we report provide new insights into how bite forces are conveyed through the most prominent teeth to allow these animals to seize prey, and initially puncture or drive cracks through their tissues. We found that both caniniform and molariform pressures scaled with positive allometry versus the expected isometric scaling value of 0.000. Notably the absolute pressures at both tooth positions were remarkably high. Values for all taxa exceeded the highest reported previously (147 MPa [21,321 psi]) for the giant extinct placoderm fish <em>Dunkleosteus</em> <a href="#pone.0031781-Anderson1" class="usa-link" aria-describedby="pone.0031781-Anderson1">[22]</a>), and pressures for some individuals were as much as 17-fold higher (<a href="#pone-0031781-t002" class="usa-link">Table 2</a>). In addition we discovered that the caniniform and molariform teeth showed similar peak pressure values within individuals and species (<a href="#pone-0031781-t002" class="usa-link">Table 2</a>). This occurred despite differing shapes and functions relative to one another (<a href="#pone-0031781-g002" class="usa-link">Figure 2</a>) and unequal bite forces (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). (The caniniform forces are 36% lower on average because they are further from the quadrate-articular joint fulcrum; <a href="#pone-0031781-t001" class="usa-link">Table 1</a>.) We suspect the reason for the similarity is that both tooth types are composed of the same dental constituents (enamel and von Ebner's dentine) and must be able to damage, and yet sustain impacts with the same tissue types when feeding. Notably, the pressure values in all taxa considerably exceed the ultimate shear strength of bone (65–71 MPa; <a href="#pone-0031781-g004" class="usa-link">Figures 4</a> and <a href="#pone-0031781-g006" class="usa-link">6</a>), the strongest of the hard constituents (incl. dentine, enamel, calcium carbonate) they encounter in their potential prey <a href="#pone.0031781-Carter1" class="usa-link" aria-describedby="pone.0031781-Carter1">[29]</a>. This holds true even during the seizing of prey underwater where initial tooth pressures could be less since jaw-closing velocity diminishes by up to two-fold from pressure and frictional drag (see <a href="#s4" class="usa-link">Materials and Methods</a>). Clearly this biomechanical capacity is integral to the dietary plasticity of all living crocodilians. It was also certainly vital to the occupation of near-shore habitats by crocodilians over millennia – although prey types changed, the materials of which they were composed did not (e.g. <a href="#pone.0031781-Erickson3" class="usa-link" aria-describedby="pone.0031781-Erickson3">[30]</a>).</p> <p>Crocodilian tooth pressures show negligible correlation with phylogeny (low K values, significant deviation from a Brownian motion model). This result suggests that convergent adaptation is contributing more signal than phylogenetic relatedness. Presumably, evolutionary changes that allowed dietary niche occupations were responsible for much of the variation. Nevertheless, ecomorph-specific tooth-pressure values are ambiguous. Only highly piscivorous <em>Gavialis gangeticus</em> and semi-piscivorous <em>Crocodylus intermedius</em> and <em>Crocodylus johnsoni</em> <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, stand out with respect to caniniform pressure generation in showing relatively high values (<a href="#pone-0031781-g004" class="usa-link">Figure 4A</a>). (This is remarkable in the cases of <em>Gavialis gangeticus</em> and <em>Crocodylus johnsoni</em>. Their most prominent caniniform teeth are located more rostrally than in all other crocodilians where bite forces are relatively low; <a href="#pone-0031781-t001" class="usa-link">Table 1</a>. Furthermore, <em>Gavialis gangeticus</em> generates the lowest relative bite forces among living crocodilians; <a href="#pone-0031781-g003" class="usa-link">Figure 3</a>.) All other crocodilian ecomorphs (molluscivores, terrestrial foragers, broad-snouted generalists, and the slender-snouted generalists – such as <em>Tomistoma schlegelii</em> and the American crocodile – <em>Crocodylus acutus</em> <a href="#pone.0031781-Webb1" class="usa-link" aria-describedby="pone.0031781-Webb1">[1]</a>, <a href="#pone.0031781-Pooley1" class="usa-link" aria-describedby="pone.0031781-Pooley1">[7]</a>) show similar values to each other that are relatively lower. What unite these ecomorphs are caniniform teeth that abruptly broaden – moving from the crown apex to the tooth neck. Should substantial, hard constituents be impacted during biting, or off-axis forces experienced, this tooth morphology provides for structural rigidity through reduced bending moments and increased area moments of inertia. However, this is afforded at the cost of rapidly diminishing tooth pressure following initial contact <a href="#pone.0031781-Unpublished1" class="usa-link" aria-describedby="pone.0031781-Unpublished1">[31]</a>. Conversely, the slender caniniform teeth of the piscivorous and semi-piscivorous ecomorphs ensure that less force is required to drive the teeth through prey. However, higher bending moments and low area moments of inertia put their long, narrow tooth crowns at risk of breakage. Tooth failure is presumably circumvented to some degree through the selection of prey with negligible hard tissues and low inertia (see above).</p> <p>Molariform tooth-pressure values vary widely among crocodilians. For example the data for the similar-sized durophagous <em>Alligator sinensis</em> and <em>Caiman latirostris</em> span much of the range for other same-sized crocodilians (<a href="#pone-0031781-g006" class="usa-link">Figure 6A</a>). No values are statistical outliers, and no definitive ecomorphological groupings exist. As mentioned above, crocodilian molariform pressures are comparable to those in the caniniform teeth. However, the bite forces at the molariform tooth positions are much higher since they are closer to the jaw's fulcrum. Because the molariform teeth are stouter, they are well suited for enduring higher resistance forces while at the same time generating pressures that, like the caniniform teeth, are initially sufficient to damage the hard constituents in their prey. Catastrophic failure of the prey's tissues is subsequently induced either by driving cracks <a href="#pone.0031781-Lucas1" class="usa-link" aria-describedby="pone.0031781-Lucas1">[21]</a> at the point of tooth engagement (the damage being more expansive in the stoutest-toothed forms), or by causing structural failure away from the point(s) of tooth engagement due to bite force alone.</p> <p>The biomechanics behind the crocodilians' remarkable and long-term occupation of niches near the water-land interface are for the first time revealed. The breadth of our findings allows us to propose an integrative model that explains the evolution of ecologically relevant phenotypic traits. Body size, and not rostral proportions, explains nearly all interspecific differences in bite-force generation. The crocodilian musculo-cranial design allows for the generation of prodigious bite forces across a broad range of sizes (<em>Gavialis gangeticus</em> is the exception; see above). This suggests that scaling mediated change in size was a primary means by which these animals gained access to new feeding resources. The rampant size changes that occurred throughout crocodilian evolution in the fossil record <a href="#pone.0031781-Brochu1" class="usa-link" aria-describedby="pone.0031781-Brochu1">[3]</a>, <a href="#pone.0031781-Brochu2" class="usa-link" aria-describedby="pone.0031781-Brochu2">[6]</a>, <a href="#pone.0031781-Brochu3" class="usa-link" aria-describedby="pone.0031781-Brochu3">[32]</a> are testament to the importance of scale-mediated changes in the feeding biomechanics of these animals.</p> <p>Changes in tooth morphology also facilitated shifts in crocodilians' diets. Tooth size and shape (i.e. cross-sectional area) dictate contact areas, which act in concert with bite forces to generate pressures. These determine performance with respect to the structure and mechanical properties of prey. Our results demonstrate that tooth pressures and snout morphology change independently of each other. We found evidence in support of ecomorphic specific performance in more piscivorous species with regard to initial tooth pressures. Others certainly exist, especially among durophagous species, but initial tooth pressures alone are insufficient to single out their biomechanical import. Our conceptual model leaves rostral shape, which is obviously very important with regard to the crocodilian diversification, to be explained more fully by its relevance to the positioning and numbers of teeth, jaw hydrodynamics, and resistance to torsion or bending during prey capture and processing <a href="#pone.0031781-Pierce1" class="usa-link" aria-describedby="pone.0031781-Pierce1">[11]</a>. Collectively, the data and methods from this study provide the quantitative biomechanical foundation for further exploration (particularly in fossil taxa) of the remarkable evolutionary success of these long-term predatory denizens of the water-land interface.</p></section><section id="s4"><h2 class="pmc_sec_title">Materials and Methods</h2> <section id="s4a"><h3 class="pmc_sec_title">Data Collection</h3> <p>This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The research protocol was approved by the Animal Care and Use Committee of The Florida State University (Permit Number: 0011). The animals were manually secured and strapped down to a testing platform prior to bite-force experimentation, and all efforts were made to minimize suffering. No animals were injured during the execution of this research.</p> <p>We tested all available sexually mature adult crocodilian specimens from research, conservation, and display specimens housed at the St. Augustine Alligator Farm Zoological Park, St. Augustine Florida, USA and Crocodylus Park, Darwin, AUS (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). In total 83 adult (sexually mature) specimens representing all 23 extant crocodilian species currently recognized by the IUCN-SSC (Species Survival Commission of the International Union for Conservation) Crocodile Specialist Group (<a href="#pone.0031781-King1" class="usa-link" aria-describedby="pone.0031781-King1">[23]</a>; size range 1.24–4.59 m, 7–531 kg) were accessed. Multiple individuals were studied for 19 species (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). Our analysis included both male and female specimens since prior studies on wild and captive <em>Alligator mississippiensis</em> bite forces revealed statistically indistinguishable performance in same-sized individuals (i.e. body mass, SVL, TL) <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a>. The results from the present study confirmed these findings (data not presented).</p> <p>The bite forces were recorded using sandwich transducers and a portable charge amplification system specifically designed for use on crocodilians <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>. Two preliminary studies on growth series of captive and wild <em>Alligator mississippiensis</em> using this system showed that specimens consistently bit at values near the yield point of the dentition (safety factor = 1.0–1.4) and hence near maximal structural capacity (Note: ∼10% of wild <em>Alligator mississippiensis</em> teeth are fractured during normal usage prior to shedding; <a href="#pone.0031781-Erickson4" class="usa-link" aria-describedby="pone.0031781-Erickson4">[33]</a>), and bite-force values for captive specimens can be used to accurately model those in wild individuals when standardized to body mass <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a>. Three to five bites were recorded for each animal, the highest of which was used in post-hoc analyses.</p> <p>Forces were measured on land with the transducer centered below either the left or right most prominent maxillary molariform tooth (located at the maxilla convexity nearer the back of the jaws; <a href="#pone-0031781-g002" class="usa-link">Figure 2</a>). This is an ecologically relevant location since it is where these animals primarily crush prey. Crocodilians stereotypically seize prey contacted by the teeth and jaws as the head is swiped to the side. They also process food on one side of the jaw. Thus, unilateral rather than bilateral tooth engagement best mimics natural feeding behavior. Additionally, unilateral crushing of prey at the molariform teeth commonly occurs with the head out of water in all species. Similarly, the seizing of prey using the caniniform teeth often occurs with the head out of water. Fortuitously the prominent molariform tooth position is at a comparable relative distance from the fulcrum across taxa, as an RMA plot of log-transformed fulcrum to molariform distance regressed against log-transformed body mass showed a scaling coefficient of 0.342±0.029 (95% CI), which is not different than isometry at 0.333. Therefore it provided a useful biomechanical standard of comparison in our testing. We took into consideration the effects of drag on force (and pressure generation; see below) during underwater feeding. Maximal velocity differences during terrestrial versus aquatic biting are no more than two-fold intraspecifically regardless of rostral form <a href="#pone.0031781-Unpublished1" class="usa-link" aria-describedby="pone.0031781-Unpublished1">[31]</a>. (Note: The effective bite force applied during sub-aquatic or terrestrial clenching bites [i.e. where the bite-force transducer or prey has already been seized and a new bite initiated] would be unaffected by drag. Our data show that the forces generated during such bites are at least 90% of the maximum values recorded during initial, defensive bites <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a>, <a href="#pone.0031781-Unpublished1" class="usa-link" aria-describedby="pone.0031781-Unpublished1">[31]</a>.)</p> <p>Standard measures of size and morphometrics pertinent to feeding biology were then recorded (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). These included body mass (BM), total length (TL), and rostral proportion (RP, = mid-rostral width/snout length [measured midway between the anterior borders of the orbits to the tip of the rostrum]). In addition, dental putty molds (Knead-A-Mold; Townsend Atelier Inc., Chattanooga, TN) were made for the most prominent caniniform tooth, the primary tooth used to initially contact and seize prey, as well as for the most prominent molariform tooth used in the crushing of prey (<a href="#pone-0031781-g002" class="usa-link">Figure 2</a>). These prominent teeth reside in alveoli at the apex of the maxilla convexities. They primarily act in isolation to initiate contact with the prey during seizing or crushing feeding behaviors. Their initial biomechanical performance can be directly linked to morphology and/or dietary ecology before the adjacent teeth become engaged as the tooth descends into prey or the padded transducer. (Note: the caniniform teeth in particular are also employed in defense and aggression where the same biomechanical performance measures studied here are also pertinent). The most pristine of any tooth pair was molded. Specimens for which both teeth were heavily damaged were not used in our analysis. Epoxy casts were made from the molds for use in post-hoc interspecific comparisons of absolute initial maximal tooth pressures.</p> <p>The casts were indented normally to a depth of one mm in modeling clay. (We found that measurements <5% crown height were imprecise for the teeth of small taxa. Because of this we opted to use the minimal depth for which repeatable measurements of area could be made for all specimens.) The indentations were digitally photographed and the realized contact area normal to the direction of loading determined using NIH Image software (ImageJ64 v.1.42q, National Institute of Health, Bethesda, MD, USA). Initial molariform tooth pressures were determined by dividing the one mm contact area for each individual's molariform tooth into its respective molariform bite-force value. Initial caniniform pressure estimates were determined by dividing the one mm contact area for each individual's caniniform tooth into its respective estimated bite-force value. We analyzed the significance of the tooth-pressure values with respect to the shear strengths of the hardest constituents found in crocodilian prey. (Note: shearing is the primary means of failure for hard materials in biological systems <a href="#pone.0031781-Carter1" class="usa-link" aria-describedby="pone.0031781-Carter1">[29]</a>.)</p></section><section id="s4b"><h3 class="pmc_sec_title">Raw Data (“TIPS”) Analyses</h3> <p>To establish the effects of body size and morphology on bite force, we established a taxon representative value of bite force at the most prominent molariform tooth for each of the 23 crocodilian species (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). For most taxa (n = 19) this was simply established using the mean maximal bite force with respect to mean body mass. These included species for which: 1) just two or fewer individuals were available for testing, or 2) species for which no statistical difference between representative values were found using either an ordinary least squares (OLS) linear-fit, or a power-law modeling of the data with body mass as the independent variable. Notably we found these to be taxa whose range of sizes in our sample was less than 70% of the size for the largest individual. However, for some taxa (i.e. <em>Alligator mississippiensis</em>, <em>Crocodylus johnsoni</em>, <em>Crocodylus porosus</em>, and <em>Osteolaemus tetraspis</em>—species for which the range of intraspecific body sizes in our sample was greater than 70% of the largest individual's size) it was necessary to account for scaling effects on bite force using power-law modeling. A moment calculation was used to infer the biting force simultaneously developed at the prominent caniniform tooth of each individual <a href="#pone.0031781-Erickson5" class="usa-link" aria-describedby="pone.0031781-Erickson5">[34]</a> (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). Taxon representative caniniform bite forces were derived using the same protocol discussed above for the molariform bite-force data (see above). For comparing taxon representative bite forces, making extrapolations to fossil taxa, and deriving residuals for subsequent analyses, OLS regressions were used.</p> <p>As with bite forces, we also established taxon representative values for caniniform and molariform contact area (<a href="#pone-0031781-t002" class="usa-link">Table 2</a>). For most taxa (n = 19), this was done by averaging the one mm mean contact area data for each species (see above). For the same four taxa in which the range of intraspecific body size was greater than 70% of the largest individual's size (see above), we accounted for scaling effects on contact area using power-law modeling. Taxon representative molariform and caniniform tooth pressures were then derived using the same protocol discussed previously (see above) for taxon representative bite forces and contact areas.</p> <p>Scaling relationships for taxon representative bite forces, as well as the taxon representative caniniform and molariform pressures, were determined using reduced major axis regressions to account for error in both the X and Y-variables, which were log-transformed. A best-fit regression and 95% confidence intervals were then constructed. Plots for which the scaling coefficient fell outside the confidence intervals of the best-fit regression were considered to be allometric. (Note: isometry for taxon representative bite forces regressed against body mass has a scaling coefficient of 0.667. This is because force increases as a square [i.e. as a function of muscle physiological cross-sectional area] while body mass, a volumetric measure, increases as a cube. On the other hand, isometric scaling of tooth pressures has a scaling coefficient of 0.000. This is because both the force and contact area parameters used to calculate tooth pressure increase as a square with respect to increases in body mass. Thus, tooth pressure is expected to remain unchanged with respect to interspecific increases in body mass among crocodilians.)</p> <p>After regressing the taxon representative bite forces against mean body mass for all species using OLS, we used the bite-force residuals to analyze the effects of rostral proportions on relative bite force independent of size for each taxon. While these results are useful for visualizing the relationships between size, morphology, and bite force, they do not take into account the phylogenetic relationships among taxa. In order to provide a visual heuristic of the pattern of evolution, all TIPs data were mapped onto the phylogeny described below under maximum likelihood using Mesquite 2.5 <a href="#pone.0031781-Midford1" class="usa-link" aria-describedby="pone.0031781-Midford1">[35]</a>. In order to account for correlations due to shared history and gain statistical rigor, we proceeded to investigate phylogenetic independent contrasts in the manner described below.</p></section><section id="s4c"><h3 class="pmc_sec_title">Phylogeny Reconstruction</h3> <p>We chose to use the exceptionally comprehensive gene database from Gatesy et al. <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a> to explore the effects of phylogeny on the character evolution of crocodilian feeding biomechanics. We acknowledge that, as with nearly all species rich phylogenies, competing hypotheses exist. Among published molecular studies some sub-clade relationships are debated (e.g. <em>Crocodylus porosus, and Crocodylus acutus</em> <a href="#pone.0031781-Meganathan1" class="usa-link" aria-describedby="pone.0031781-Meganathan1">[36]</a>–<a href="#pone.0031781-Meredith1" class="usa-link" aria-describedby="pone.0031781-Meredith1">[39]</a>). Nonetheless, the comprehensive sampling of genetic data as in Gatesy et al. <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a> has yet to occur to enable more rigorous comparisons across all taxa. Morphologically derived trees provide consistent hypotheses with regard to the position of <em>Gavialis gangeticus</em> as outside of Crocodyloidea <a href="#pone.0031781-Brochu1" class="usa-link" aria-describedby="pone.0031781-Brochu1">[3]</a>, <a href="#pone.0031781-Brochu2" class="usa-link" aria-describedby="pone.0031781-Brochu2">[6]</a>, and some morphology-only <a href="#pone.0031781-Brochu2" class="usa-link" aria-describedby="pone.0031781-Brochu2">[6]</a>, <a href="#pone.0031781-Brochu4" class="usa-link" aria-describedby="pone.0031781-Brochu4">[40]</a> and combined molecular and morphology analyses <a href="#pone.0031781-McAliley1" class="usa-link" aria-describedby="pone.0031781-McAliley1">[41]</a> support the African slender-snouted crocodile (<em>Mecistops cataphractus</em>) as sister to <em>Crocodylus</em> instead of <em>Osteolaemus tetraspis</em> <a href="#pone.0031781-Brochu2" class="usa-link" aria-describedby="pone.0031781-Brochu2">[6]</a>. Regardless, we are confident the tree used here is the best available estimate of the true phylogeny that also contains time-correlated branch lengths (necessary for PIC analysis). Character mapping and exploring the potential evolutionary and ecological ramifications of our data using other competing hypotheses is beyond the scope of the present study, but will be the topic of future analyses.</p> <p>For our study, an aligned DNA sequence matrix was obtained from John Gatesy (University of California, Santa Barbara), consisting of published sequences for the nuclear genes RAG-1, BDNF, ATP7A, LDHa, c-myc, c-mos, DMP1, ODC, and 18S/28S rflp, and portions of the mitochondrial genes nd6, cyt b, the intervening glutamine tRNA, control region, 12S, and 16S <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a>. Because the published trees did not include branch lengths, and were not ultrametric (i.e. proportional to time), we re-estimated the phylogeny. Some species were not represented for all genes. Most notable was the New Guinea crocodile (<em>Crocodylus novaeguineae</em>) that included only the ND6/cyt b and 18S/28S regions. No sequence data were available for <em>Caiman yacare</em>, and so it was not included in the phylogeny, nor in subsequent phylogenetic independent contrasts (PIC). (Note: it was, however, included in analyses of the raw [TIPs] data.) We followed Gatesy <em>et al.</em> <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a> in designating Paleognathae and Neognathae as outgroups in all phylogenetic analyses. However these were pruned from the tree prior to conducting the PIC analyses. Alignments were checked by eye. Small modifications were made to maintain codon integrity in reference to the translated amino acid sequence using MacClade <a href="#pone.0031781-Maddison1" class="usa-link" aria-describedby="pone.0031781-Maddison1">[42]</a>, but sequences otherwise conformed to the published alignments. A maximum likelihood (ML) search was conducted using PAUP <a href="#pone.0031781-Swofford1" class="usa-link" aria-describedby="pone.0031781-Swofford1">[43]</a> under the GTR+I+G model as indicated by Modeltest <a href="#pone.0031781-Posada1" class="usa-link" aria-describedby="pone.0031781-Posada1">[44]</a> and the Akaike Information Criterion. Parameters were estimated from a randomly chosen tree among the most parsimonious trees found under equal weighting parsimony. Starting trees included the set of most parsimonious trees in addition to 10 random addition sequence replicates. All searches found the same single tree (<a href="#pone-0031781-g001" class="usa-link">Figure 1</a>), congruent with the slightly less resolved tree in Gatesy et al. <a href="#pone.0031781-Gatesy1" class="usa-link" aria-describedby="pone.0031781-Gatesy1">[2]</a>, and identical to that in the more recent Gatesy and Amato <a href="#pone.0031781-Gatesy2" class="usa-link" aria-describedby="pone.0031781-Gatesy2">[45]</a> analysis with the exception of our tree resolving one trichotomy near the tip in <em>Crocodylus</em>. The ML tree was made ultrametric using penalized likelihood in r8s <a href="#pone.0031781-Sanderson1" class="usa-link" aria-describedby="pone.0031781-Sanderson1">[46]</a>, <a href="#pone.0031781-Sanderson2" class="usa-link" aria-describedby="pone.0031781-Sanderson2">[47]</a> and the ML branch lengths. Cross validation was conducted on the ML tree using a range of smoothing parameters from 1 to 1000. A smoothing parameter value of 3.2 was found to minimize deviations and was the value used in the final analysis.</p></section><section id="s4d"><h3 class="pmc_sec_title">Phylogenetic Independent Contrasts</h3> <p>All morphological and mechanical variables (see <a href="#pone-0031781-t001" class="usa-link">Tables 1</a> and <a href="#pone-0031781-t002" class="usa-link">2</a>) were log-transformed with the exception of rostral proportions (RP). Transformations were done to normalize these data, which spanned a large, 21-fold size range in mean body mass (<a href="#pone-0031781-t001" class="usa-link">Table 1</a>). Because rostral proportions are a ratio, and therefore are already normalized to body size, log-transformation was unnecessary. These proportions were not significantly correlated with size, unlike all other variables. Phylogenetic signal was estimated by the K statistic using the picante package <a href="#pone.0031781-Kembel1" class="usa-link" aria-describedby="pone.0031781-Kembel1">[48]</a> in R <a href="#pone.0031781-R1" class="usa-link" aria-describedby="pone.0031781-R1">[49]</a>. K statistics ranged from 0.347 to 0.838. A value of 1.0 indicates these data are fit by a Brownian motion model, whereas values close to 0 indicate closely related taxa are less similar than expected under Brownian motion, as might be caused by adaptation or measurement error <a href="#pone.0031781-Blomberg1" class="usa-link" aria-describedby="pone.0031781-Blomberg1">[50]</a>. All variables exhibited significant phylogenetic signal (K>0.5) except log-molariform contact area and the log-pressure variables (K = 0.347–0.443; p = 0.209–0.344). Caniniform and molariform pressures were mapped onto the phylogeny using the Mk1 model for likelihood in Mesquite 2.5 <a href="#pone.0031781-Midford1" class="usa-link" aria-describedby="pone.0031781-Midford1">[35]</a>. PIC analyses were conducted using the ultrametric tree with the PDAP module <a href="#pone.0031781-Maddison2" class="usa-link" aria-describedby="pone.0031781-Maddison2">[51]</a> in Mesquite 2.5 <a href="#pone.0031781-Midford1" class="usa-link" aria-describedby="pone.0031781-Midford1">[35]</a>. The contrasts were standardized through division with their standard deviations (square-root of summed branch lengths). This effectively converted them to evolutionary rates. PDAP diagnostics (standardized contrasts regressed against their standard deviations) showed that only log-molariform contact area and log-caniniform pressure deviated significantly from a Brownian motion model (p<0.05). Because the tree contained one trichotomy, the degrees of freedom for the diagnostics were reduced by one. Since bite force was strongly correlated with body mass for both raw data (R<sup>2</sup> = 0.92) and phylogenetically corrected log-transformed data (R<sup>2</sup> = 0.87), we first created size-standardized variables. This was achieved by regressing contrasts of mean rostral proportions as well as log-transformed taxon representative bite forces, tooth contact areas, and tooth pressures against contrasts of log-mass and saved the residuals. To remove the effects of tooth size, the size-standardized residuals for pressure were also regressed against the size-standardized residuals of contact area. These size- and contact area-standardized residuals were saved. This effectively removed the evolutionary variance in pressure associated with changes in body mass and tooth cross-sectional area. These residuals for performance measures were then regressed against the rostral proportions. All regressions on PICs were constrained to pass through the origin. Throughout, we report TIPs results for ease of visualization, but due to non-independence of the raw data, statistical significance is reported only for PICs.</p></section><section id="s4e"><h3 class="pmc_sec_title">Estimations of Bite Forces in Fossil Crocodilians and Large Extant Individuals</h3> <p>Our range of bite-force estimates for 6.7 m specimens of <em>Crocodylus porosus</em> was based upon the interspecific regression of mean body mass versus mean bite force (Y<sub>(force, N)</sub> = 29.632x<sub>(body mass, kg)</sub>+569.35; R<sup>2</sup> = 0.92; see <a href="#pone-0031781-g003" class="usa-link">Figure 3A</a>) with an estimated mass of 1,308 kg from the intraspecific regressions of wild <em>Crocodylus porosus</em> from Webb and Messel <a href="#pone.0031781-Webb2" class="usa-link" aria-describedby="pone.0031781-Webb2">[52]</a>. A second bite-force estimate was acquired using an intraspecific regression for a captive growth series of this taxon (range = 0.96–531 kg; <a href="#pone.0031781-Unpublished1" class="usa-link" aria-describedby="pone.0031781-Unpublished1">[31]</a>) where y<sub>(bite force, N)</sub> = 115.39x<sub>(body mass, kg)</sub> <sup>0.7629</sup>, R<sup>2</sup> = 0.98). Note: Our previous research has shown that bite-force generation is statistically indistinguishable between same-sized (i.e. body mass, SVL, or TL) captive and wild <em>Alligator mississippiensis</em> <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a>.</p> <p>Our estimates of the upper and lower historical bounds of adult crocodilian bite forces were based on the interspecific regression of mean mass versus mean bite force (Y<sub>(force, N)</sub> = 29.632x<sub>(mass, kg)</sub>+569.35; R<sup>2</sup> = 0.92; see <a href="#pone-0031781-g003" class="usa-link">Figure 3A</a>) with an estimated mean mass from our interspecific regression of captive crocodilians reduced by 25% <a href="#pone.0031781-Erickson1" class="usa-link" aria-describedby="pone.0031781-Erickson1">[14]</a>, <a href="#pone.0031781-Erickson2" class="usa-link" aria-describedby="pone.0031781-Erickson2">[15]</a> to account for the lesser mean body mass of wild individuals compared to captives of equal TL. We used the 0.8 m TL <em>Procaimanoidea kayi</em> <a href="#pone.0031781-Mook1" class="usa-link" aria-describedby="pone.0031781-Mook1">[27]</a> to represent the lowermost bound of known size for Crocodylia. The 11 m TL <em>Deinosuchus riograndensis</em> <a href="#pone.0031781-Farlow1" class="usa-link" aria-describedby="pone.0031781-Farlow1">[28]</a> was used to represent the upper bound. The mean largest adult body masses for these taxa were estimated from our interspecific regression of mean mass and TL for adults of extant taxa (Y<sub>(body mass, kg)</sub> = 5.00x<sub>(total length, m)</sub> <sup>2.846</sup>; R<sup>2</sup> = 0.93). (Note: the upper bound bite-force estimate for <em>Deinosuchus riograndensis</em> is more tenuous since the largest known fossil crocodilian specimens greatly exceed the neontological size range studied here.)</p></section></section><section id="ack1" class="ack"><h2 class="pmc_sec_title">Acknowledgments</h2> <p>This research is dedicated to the late T. Hunter and J. B. Thorbjarnarson. Both provided invaluable insights and assistance for our study. A special thanks goes out to D. C. Drysdale for generously allowing scientific access to the entirety of his crocodilian specimens at the St. Augustine Alligator Farm Zoological Park. We also thank the curatorial staff members of St. Augustine Alligator Farm Zoological Park and Crocodylus Park. J. Gatesy generously allowed access to his comprehensive data on the phylogeny for the Crocodylia. C. Brochu and Wann Langston provided helpful discussions about fossil crocodilian specimens, historical size range, systematics, and taxonomy. S. Deban assisted with the gathering and analysis of data on underwater jaw closure. K. Womble produced the graphics.</p></section><section id="fn-group1" class="fn-group"><h2 class="pmc_sec_title">Footnotes</h2> <div class="fn-group p font-secondary-light font-sm"> <div class="fn p" id="fn23"><p><strong>Competing Interests: </strong>The authors have declared that no competing interests exist.</p></div> <div class="fn p" id="fn24"><p><strong>Funding: </strong>This research was partially supported by a grant from the Committee for Research and Exploration of the National Geographic Society presented to GME, National Science Foundation grants, IOB-0623791/BIO326U-02 presented to AKL, EAR 04418649 and EAR 0959029 presented to GME, and DEB-0841447 to SJS, and finally research funds from the College of Arts and Sciences at FSU and Department of Biology at UF. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.</p></div> </div></section><section id="ref-list1" class="ref-list"><h2 class="pmc_sec_title">References</h2> <section id="ref-list1_sec2"><ul class="ref-list font-sm" style="list-style-type:none"> <li id="pone.0031781-Webb1"> <span class="label">1.</span><cite>Webb G, Manolis C. Crocodiles of Australia. New South Wales: Reed; 1989. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Crocodiles%20of%20Australia&author=G%20Webb&author=C%20Manolis&publication_year=1989&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Gatesy1"> <span class="label">2.</span><cite>Gatesy J, Baker RH, Hayashi C. Inconsistencies in arguments for the supertree approach: supermatrices versus supertrees of Crocodylia. Sys Bio. 2004;53:342–355. doi: 10.1080/10635150490423971.</cite> [<a href="https://doi.org/10.1080/10635150490423971" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/15205058/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Sys%20Bio&title=Inconsistencies%20in%20arguments%20for%20the%20supertree%20approach:%20supermatrices%20versus%20supertrees%20of%20Crocodylia.&author=J%20Gatesy&author=RH%20Baker&author=C%20Hayashi&volume=53&publication_year=2004&pages=342-355&pmid=15205058&doi=10.1080/10635150490423971&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Brochu1"> <span class="label">3.</span><cite>Brochu CA. Crocodylian snouts in space and time: phylogenetic approaches toward adaptive radiation. Amer Zool. 2001;41:564–585.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Amer%20Zool&title=Crocodylian%20snouts%20in%20space%20and%20time:%20phylogenetic%20approaches%20toward%20adaptive%20radiation.&author=CA%20Brochu&volume=41&publication_year=2001&pages=564-585&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Frey1"> <span class="label">4.</span><cite>Frey E. Ecology, locomotion and tail muscle anatomy of crocodiles. Neues Jahrb Geol Paläont Abh. 1982;164:194–199.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Neues%20Jahrb%20Geol%20Pal%C3%A4ont%20Abh&title=Ecology,%20locomotion%20and%20tail%20muscle%20anatomy%20of%20crocodiles.&author=E%20Frey&volume=164&publication_year=1982&pages=194-199&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Parrish1"> <span class="label">5.</span><cite>Parrish JM. The origin of crocodilian locomotion. Paleobiology. 1987;13:396–414.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Paleobiology&title=The%20origin%20of%20crocodilian%20locomotion.&author=JM%20Parrish&volume=13&publication_year=1987&pages=396-414&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Brochu2"> <span class="label">6.</span><cite>Brochu CA. Phylogenetic approaches toward crocodylian history. Ann Rev Ear Plan Sci. 2003;31:357–397.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Ann%20Rev%20Ear%20Plan%20Sci&title=Phylogenetic%20approaches%20toward%20crocodylian%20history.&author=CA%20Brochu&volume=31&publication_year=2003&pages=357-397&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Pooley1"> <span class="label">7.</span><cite>Pooley AC. Food and feeding habits. In: Ross CA, editor. Crocodiles and Alligators. New York: Facts on File; 1989. pp. 76–91.</cite> [<a href="https://scholar.google.com/scholar_lookup?title=Crocodiles%20and%20Alligators&author=AC%20Pooley&publication_year=1989&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Thorbjarnarson1"> <span class="label">8.</span><cite>Thorbjarnarson JB. Notes on the feeding behavior of the gharial (Gavialis gangeticus) under semi-natural conditions. J Herp. 1990;24:99–100.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Herp&title=Notes%20on%20the%20feeding%20behavior%20of%20the%20gharial%20(Gavialis%20gangeticus)%20under%20semi-natural%20conditions.&author=JB%20Thorbjarnarson&volume=24&publication_year=1990&pages=99-100&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Busbey1"> <span class="label">9.</span><cite>Busbey AB. The structural consequences of skull flattening in crocodilians. In: Thomason JJ, editor. Functional Morphology in Vertebrate Paleontology. New York: University of Cambridge Press; 1995. pp. 173–192.</cite> [<a href="https://scholar.google.com/scholar_lookup?title=Functional%20Morphology%20in%20Vertebrate%20Paleontology&author=AB%20Busbey&publication_year=1995&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-McHenry1"> <span class="label">10.</span><cite>McHenry CR, Clausen PD, Daniel WJT, Meers MB, Pendharkar A. The biomechanics of the rostrum in crocodilians: a comparative analysis using finite element modelling. Anat Rec. 2006;288:827–849. doi: 10.1002/ar.a.20360.</cite> [<a href="https://doi.org/10.1002/ar.a.20360" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/16835925/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Anat%20Rec&title=The%20biomechanics%20of%20the%20rostrum%20in%20crocodilians:%20a%20comparative%20analysis%20using%20finite%20element%20modelling.&author=CR%20McHenry&author=PD%20Clausen&author=WJT%20Daniel&author=MB%20Meers&author=A%20Pendharkar&volume=288&publication_year=2006&pages=827-849&pmid=16835925&doi=10.1002/ar.a.20360&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Pierce1"> <span class="label">11.</span><cite>Pierce SE, Angielczyk KD, Rayfield EJ. Patterns of morphospace occupation and mechanical performance in extant crocodilian skulls: a combined geometric morphometric and finite element modeling approach. J Morph. 2008;269:840–864. doi: 10.1002/jmor.10627.</cite> [<a href="https://doi.org/10.1002/jmor.10627" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/18496856/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Morph&title=Patterns%20of%20morphospace%20occupation%20and%20mechanical%20performance%20in%20extant%20crocodilian%20skulls:%20a%20combined%20geometric%20morphometric%20and%20finite%20element%20modeling%20approach.&author=SE%20Pierce&author=KD%20Angielczyk&author=EJ%20Rayfield&volume=269&publication_year=2008&pages=840-864&pmid=18496856&doi=10.1002/jmor.10627&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Borteiro1"> <span class="label">12.</span><cite>Borteiro C, Gutierrez F, Tedros M, Kolenc F. Food habits of the broad-snouted caiman (Caiman latirostris: Crocodylia, Alligatoridae) in northwestern Uruguay. Studies Neoptrop Fauna Envir. 2009;44:31–36.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Studies%20Neoptrop%20Fauna%20Envir&title=Food%20habits%20of%20the%20broad-snouted%20caiman%20(Caiman%20latirostris:%20Crocodylia,%20Alligatoridae)%20in%20northwestern%20Uruguay.&author=C%20Borteiro&author=F%20Gutierrez&author=M%20Tedros&author=F%20Kolenc&volume=44&publication_year=2009&pages=31-36&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Magnusson1"> <span class="label">13.</span><cite>Magnusson WE, Lima AP. The ecology of a cryptic predator Paleosuchus trigonatus in a tropical rainforest. J Herp. 1991;25:41–48.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Herp&title=The%20ecology%20of%20a%20cryptic%20predator%20Paleosuchus%20trigonatus%20in%20a%20tropical%20rainforest.&author=WE%20Magnusson&author=AP%20Lima&volume=25&publication_year=1991&pages=41-48&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Erickson1"> <span class="label">14.</span><cite>Erickson GM, Lappin AK, Vliet KA. The Ontogeny of bite-force performance in American alligator (Alligator mississippiensis). J Zool Lond. 2003;260:317–327.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Zool%20Lond&title=The%20Ontogeny%20of%20bite-force%20performance%20in%20American%20alligator%20(Alligator%20mississippiensis).&author=GM%20Erickson&author=AK%20Lappin&author=KA%20Vliet&volume=260&publication_year=2003&pages=317-327&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Erickson2"> <span class="label">15.</span><cite>Erickson GM, Lappin AK, Parker T, Vliet KA. Comparison of bite-force performance between long-term captive and wild captured American alligators (Alligator mississippiensis). J Zool Lond. 2004;262:21–28.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Zool%20Lond&title=Comparison%20of%20bite-force%20performance%20between%20long-term%20captive%20and%20wild%20captured%20American%20alligators%20(Alligator%20mississippiensis).&author=GM%20Erickson&author=AK%20Lappin&author=T%20Parker&author=KA%20Vliet&volume=262&publication_year=2004&pages=21-28&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Neill1"> <span class="label">16.</span><cite>Neill WT. The Last of the Ruling Reptiles: Alligators, Crocodiles and their Kin. Ithaca: Columbia University Press; 1971. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=The%20Last%20of%20the%20Ruling%20Reptiles:%20Alligators,%20Crocodiles%20and%20their%20Kin&author=WT%20Neill&publication_year=1971&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Iordansky1"> <span class="label">17.</span><cite>Iordansky NN. The jaw muscles of the crocodiles and some relating structures of the crocodilian skull. Anat Anz. 1964;115:256–280.</cite> [<a href="https://pubmed.ncbi.nlm.nih.gov/14327484/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Anat%20Anz&title=The%20jaw%20muscles%20of%20the%20crocodiles%20and%20some%20relating%20structures%20of%20the%20crocodilian%20skull.&author=NN%20Iordansky&volume=115&publication_year=1964&pages=256-280&pmid=14327484&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Schumacher1"> <span class="label">18.</span><cite>Schumacher GH. The head muscles and hyolaryngeal skeleton of turtles and crocodilians. In: Gans C, Parsons TS, editors. Biology of the Reptilia, Volume 4. London: Academic Press; 1973. pp. 101–199.</cite> [<a href="https://scholar.google.com/scholar_lookup?title=Biology%20of%20the%20Reptilia,%20Volume%204&author=GH%20Schumacher&publication_year=1973&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Endo1"> <span class="label">19.</span><cite>Endo H, Aoki R, Taru H, Kimura J, Sasaki M, et al. Comparative functional morphology of the masticatory apparatus in the long-snouted crocodiles. Anat Histol Embr. 2002;31:206–213. doi: 10.1046/j.1439-0264.2002.00396.x.</cite> [<a href="https://doi.org/10.1046/j.1439-0264.2002.00396.x" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/12196262/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Anat%20Histol%20Embr&title=Comparative%20functional%20morphology%20of%20the%20masticatory%20apparatus%20in%20the%20long-snouted%20crocodiles.&author=H%20Endo&author=R%20Aoki&author=H%20Taru&author=J%20Kimura&author=M%20Sasaki&volume=31&publication_year=2002&pages=206-213&pmid=12196262&doi=10.1046/j.1439-0264.2002.00396.x&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Snodgrass1"> <span class="label">20.</span><cite>Snodgrass JM, Gilbert PW. A shark-bite meter. In: Gilbert PW, Mathewson RF, Rall DP, editors. Sharks, Skates, and Rays. Baltimore: Johns Hopkins University Press; 1967. pp. 331–337.</cite> [<a href="https://scholar.google.com/scholar_lookup?title=Sharks,%20Skates,%20and%20Rays&author=JM%20Snodgrass&author=PW%20Gilbert&publication_year=1967&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Lucas1"> <span class="label">21.</span><cite>Lucas PW. Dental Functional Morphology: How Teeth Work. New York: Cambridge University Press; 2004. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Dental%20Functional%20Morphology:%20How%20Teeth%20Work&author=PW%20Lucas&publication_year=2004&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Anderson1"> <span class="label">22.</span><cite>Anderson PS, Westneat MW. Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator. Biol Lett. 2006;3:76–79. doi: 10.1098/rsbl.2006.0569.</cite> [<a href="https://doi.org/10.1098/rsbl.2006.0569" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="/articles/PMC2373817/" class="usa-link">PMC free article</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/17443970/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Biol%20Lett&title=Feeding%20mechanics%20and%20bite%20force%20modelling%20of%20the%20skull%20of%20Dunkleosteus%20terrelli,%20an%20ancient%20apex%20predator.&author=PS%20Anderson&author=MW%20Westneat&volume=3&publication_year=2006&pages=76-79&pmid=17443970&doi=10.1098/rsbl.2006.0569&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-King1"> <span class="label">23.</span><cite>King FW, Burke RL. Crocodilian, Tuatara and Turtle Species of the World: A Taxonomic Reference. Wash. D.C.: Assoc. Syst. Collections; 1989. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Crocodilian,%20Tuatara%20and%20Turtle%20Species%20of%20the%20World:%20A%20Taxonomic%20Reference&author=FW%20King&author=RL%20Burke&publication_year=1989&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Alexander1"> <span class="label">24.</span><cite>Alexander RMcN. Factors of safety in the structures of animals. Sci Prog. 1981;67:109–130.</cite> [<a href="https://pubmed.ncbi.nlm.nih.gov/7013065/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Sci%20Prog&title=Factors%20of%20safety%20in%20the%20structures%20of%20animals.&author=RMcN%20Alexander&volume=67&publication_year=1981&pages=109-130&pmid=7013065&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Huchzermeyer1"> <span class="label">25.</span><cite>Huchzermeyer FW. Crocodiles: Biology, Husbandry and Disease. South Africa: CABI Publishing; 2003. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Crocodiles:%20Biology,%20Husbandry%20and%20Disease&author=FW%20Huchzermeyer&publication_year=2003&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Binder1"> <span class="label">26.</span><cite>Binder WJ, van Valkenburgh B. Development of bite strength and feeding behavior in juvenile spotted hyenas (Crocuta crocuta). J Zool Lond. 2000;252:273–283.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Zool%20Lond&title=Development%20of%20bite%20strength%20and%20feeding%20behavior%20in%20juvenile%20spotted%20hyenas%20(Crocuta%20crocuta).&author=WJ%20Binder&author=B%20van%20Valkenburgh&volume=252&publication_year=2000&pages=273-283&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Mook1"> <span class="label">27.</span><cite>Mook CC. A new crocodilian, Hassiacosuchus kayi, from the Bridger Eocene beds of Wyoming. Ann Carnegii Mus. 1941;28:207–220.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Ann%20Carnegii%20Mus&title=A%20new%20crocodilian,%20Hassiacosuchus%20kayi,%20from%20the%20Bridger%20Eocene%20beds%20of%20Wyoming.&author=CC%20Mook&volume=28&publication_year=1941&pages=207-220&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Farlow1"> <span class="label">28.</span><cite>Farlow JO, Hurlburt GR, Elsey RM, Britton ARC, Langston W., Jr Femoral dimensions and body size of Alligator mississsippiensis: estimating the size of mesoeucrocodylians. J Vert Paleo. 2005;25:354–369.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Vert%20Paleo&title=Femoral%20dimensions%20and%20body%20size%20of%20Alligator%20mississsippiensis:%20estimating%20the%20size%20of%20mesoeucrocodylians.&author=JO%20Farlow&author=GR%20Hurlburt&author=RM%20Elsey&author=ARC%20Britton&author=W%20Langston&volume=25&publication_year=2005&pages=354-369&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Carter1"> <span class="label">29.</span><cite>Carter DR, Beaupré GS. Skeletal Function and Form: Mechanobiology of Skeletal Development, Aging, and Regeneration. New York: Cambridge University Press; 2001. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Skeletal%20Function%20and%20Form:%20Mechanobiology%20of%20Skeletal%20Development,%20Aging,%20and%20Regeneration&author=DR%20Carter&author=GS%20Beaupr%C3%A9&publication_year=2001&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Erickson3"> <span class="label">30.</span><cite>Erickson GM, Catanese J, III, Keaveny T. Evolution of the biomechanical material properties of the femur. Anat Rec. 2002;268:115–124. doi: 10.1002/ar.10145.</cite> [<a href="https://doi.org/10.1002/ar.10145" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/12221717/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Anat%20Rec&title=Evolution%20of%20the%20biomechanical%20material%20properties%20of%20the%20femur.&author=GM%20Erickson&author=J%20Catanese&author=T%20Keaveny&volume=268&publication_year=2002&pages=115-124&pmid=12221717&doi=10.1002/ar.10145&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Unpublished1"> <span class="label">31.</span><cite> Unpublished data and personal observations of GME and PMG.</cite> </li> <li id="pone.0031781-Brochu3"> <span class="label">32.</span><cite>Brochu CA. Phylogenetics, taxonomy, and historical biogeography of Alligatoroidea. J Vert Paleo Mem. 1999;19:9–100.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Vert%20Paleo%20Mem&title=Phylogenetics,%20taxonomy,%20and%20historical%20biogeography%20of%20Alligatoroidea.&author=CA%20Brochu&volume=19&publication_year=1999&pages=9-100&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Erickson4"> <span class="label">33.</span><cite>Erickson GM. Toothlessness in American alligators. Copeia. 1996;1996:739–743.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Copeia&title=Toothlessness%20in%20American%20alligators.&author=GM%20Erickson&volume=1996&publication_year=1996&pages=739-743&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Erickson5"> <span class="label">34.</span><cite>Erickson GM, Van Kirk SD, Su J, Levenston ME, Caler WE, et al. Bite-force estimation for Tyrannosaurus rex from tooth-marked bones. Nature. 1996;382:706–708.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Nature&title=Bite-force%20estimation%20for%20Tyrannosaurus%20rex%20from%20tooth-marked%20bones.&author=GM%20Erickson&author=SD%20Van%20Kirk&author=J%20Su&author=ME%20Levenston&author=WE%20Caler&volume=382&publication_year=1996&pages=706-708&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Midford1"> <span class="label">35.</span><cite>Midford PE, Garland TJ, Maddison WP. 2008. PDAP:PDTREE package for Mesquite 1.13 ed.</cite> </li> <li id="pone.0031781-Meganathan1"> <span class="label">36.</span><cite>Meganathan PR, Dubey B, Batzer MA, Ray DA, Haque I. Molecular phylogenetic analyses of genus Crocodylus (Eusuchia, Crocodylia, Crocodylidae) and the taxonomic position of Crocodylus porosus. Molec Phylog Evol. 2010;57:393–402. doi: 10.1016/j.ympev.2010.06.011.</cite> [<a href="https://doi.org/10.1016/j.ympev.2010.06.011" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/20601012/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Phylog%20Evol&title=Molecular%20phylogenetic%20analyses%20of%20genus%20Crocodylus%20(Eusuchia,%20Crocodylia,%20Crocodylidae)%20and%20the%20taxonomic%20position%20of%20Crocodylus%20porosus.&author=PR%20Meganathan&author=B%20Dubey&author=MA%20Batzer&author=DA%20Ray&author=I%20Haque&volume=57&publication_year=2010&pages=393-402&pmid=20601012&doi=10.1016/j.ympev.2010.06.011&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-MilinGarca1"> <span class="label">37.</span><cite>Milián-García Y, Venegas-Anaya M, Frias-Soler R, Crawford AJ, Ramos-Targarona R, et al. Evolutionary history of Cuban crocodiles Crocodylus rhombifer and Crocodylus acutus inferred from multilocus markers. J Exp Zool. 2011;315A:358–375. doi: 10.1002/jez.683.</cite> [<a href="https://doi.org/10.1002/jez.683" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/21462351/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=J%20Exp%20Zool&title=Evolutionary%20history%20of%20Cuban%20crocodiles%20Crocodylus%20rhombifer%20and%20Crocodylus%20acutus%20inferred%20from%20multilocus%20markers.&author=Y%20Mili%C3%A1n-Garc%C3%ADa&author=M%20Venegas-Anaya&author=R%20Frias-Soler&author=AJ%20Crawford&author=R%20Ramos-Targarona&volume=315A&publication_year=2011&pages=358-375&pmid=21462351&doi=10.1002/jez.683&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Man1"> <span class="label">38.</span><cite>Man Z, Yishu W, Peng Y, Xiaobing W. Crocodilian phylogeny inferred from twelve mitochondrial protein-coding genes, with new complete mitochondrial genomic sequences for Crocodylus acutus and Crocodylus novaeguineae. Molec Phylog Evol. 2011;60:62–67. doi: 10.1016/j.ympev.2011.03.029.</cite> [<a href="https://doi.org/10.1016/j.ympev.2011.03.029" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/21463698/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Phylog%20Evol&title=Crocodilian%20phylogeny%20inferred%20from%20twelve%20mitochondrial%20protein-coding%20genes,%20with%20new%20complete%20mitochondrial%20genomic%20sequences%20for%20Crocodylus%20acutus%20and%20Crocodylus%20novaeguineae.&author=Z%20Man&author=W%20Yishu&author=Y%20Peng&author=W%20Xiaobing&volume=60&publication_year=2011&pages=62-67&pmid=21463698&doi=10.1016/j.ympev.2011.03.029&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Meredith1"> <span class="label">39.</span><cite>Meredith RW, Hekkala ER, Amato G, Gatesy J. A phylogenetic hypothesis for Crocodylus (crocodylia) based on mitochondrial DNA: Evidence for a trans-Atlantic voyage from Africa to the New World. Molec Phylog Evol. 2011;60:183–191. doi: 10.1016/j.ympev.2011.03.026.</cite> [<a href="https://doi.org/10.1016/j.ympev.2011.03.026" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/21459152/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Phylog%20Evol&title=A%20phylogenetic%20hypothesis%20for%20Crocodylus%20(crocodylia)%20based%20on%20mitochondrial%20DNA:%20Evidence%20for%20a%20trans-Atlantic%20voyage%20from%20Africa%20to%20the%20New%20World.&author=RW%20Meredith&author=ER%20Hekkala&author=G%20Amato&author=J%20Gatesy&volume=60&publication_year=2011&pages=183-191&pmid=21459152&doi=10.1016/j.ympev.2011.03.026&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Brochu4"> <span class="label">40.</span><cite>Brochu CA, Njau J, Blumenschine RJ, Densmore LD. A new horned crocodile from the Plio-Pleistocene hominid sites at Olduvai Gorge, Tanzania. PLoS ONE. 2010;5:e9333. doi: 10.1371/journal.pone.0009333.</cite> [<a href="https://doi.org/10.1371/journal.pone.0009333" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="/articles/PMC2827537/" class="usa-link">PMC free article</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/20195356/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=PLoS%20ONE&title=A%20new%20horned%20crocodile%20from%20the%20Plio-Pleistocene%20hominid%20sites%20at%20Olduvai%20Gorge,%20Tanzania.&author=CA%20Brochu&author=J%20Njau&author=RJ%20Blumenschine&author=LD%20Densmore&volume=5&publication_year=2010&pages=e9333&pmid=20195356&doi=10.1371/journal.pone.0009333&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-McAliley1"> <span class="label">41.</span><cite>McAliley LR, Willis RE, Ray DA, White PS, Brochu CA, et al. Are crocodiles really monophyletic?—Evidence for subdivisions from sequence and morphological data. Molec Phylog Evol. 2006;39:16–32. doi: 10.1016/j.ympev.2006.01.012.</cite> [<a href="https://doi.org/10.1016/j.ympev.2006.01.012" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/16495085/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Phylog%20Evol&title=Are%20crocodiles%20really%20monophyletic?%E2%80%94Evidence%20for%20subdivisions%20from%20sequence%20and%20morphological%20data.&author=LR%20McAliley&author=RE%20Willis&author=DA%20Ray&author=PS%20White&author=CA%20Brochu&volume=39&publication_year=2006&pages=16-32&pmid=16495085&doi=10.1016/j.ympev.2006.01.012&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Maddison1"> <span class="label">42.</span><cite>Maddison DR, Maddison WP. 2000. MacClade 4: Analysis of Phylogeny and Character Evolution (Sinauer Associates, Sunderland, Massachusetts)</cite> </li> <li id="pone.0031781-Swofford1"> <span class="label">43.</span><cite>Swofford DL. 2002. PAUP*: Phylogenetic Analysis Using Parsimony (and Other Methods) 4.0 Beta (Sinauer Associates, Sunderland, Massachusetts)</cite> </li> <li id="pone.0031781-Posada1"> <span class="label">44.</span><cite>Posada D, Crandall KA. Modeltest: testing the model of DNA substitution. Bioinf. 1998;14:817–818. doi: 10.1093/bioinformatics/14.9.817.</cite> [<a href="https://doi.org/10.1093/bioinformatics/14.9.817" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/9918953/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Bioinf&title=Modeltest:%20testing%20the%20model%20of%20DNA%20substitution.&author=D%20Posada&author=KA%20Crandall&volume=14&publication_year=1998&pages=817-818&pmid=9918953&doi=10.1093/bioinformatics/14.9.817&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Gatesy2"> <span class="label">45.</span><cite>Gatesy J, Amato G. The rapid accumulation of consistent molecular support for intergeneric crocodilian relationships. Molec Phylog Evol. 2008;48:1232–1237. doi: 10.1016/j.ympev.2008.02.009.</cite> [<a href="https://doi.org/10.1016/j.ympev.2008.02.009" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/18372192/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Phylog%20Evol&title=The%20rapid%20accumulation%20of%20consistent%20molecular%20support%20for%20intergeneric%20crocodilian%20relationships.&author=J%20Gatesy&author=G%20Amato&volume=48&publication_year=2008&pages=1232-1237&pmid=18372192&doi=10.1016/j.ympev.2008.02.009&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Sanderson1"> <span class="label">46.</span><cite>Sanderson MJ. Estimating absolute rates of molecular evolution and divergence times: a penalized likelihood approach. Molec Biol Evol. 2002;19:101–109. doi: 10.1093/oxfordjournals.molbev.a003974.</cite> [<a href="https://doi.org/10.1093/oxfordjournals.molbev.a003974" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/11752195/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Molec%20Biol%20Evol&title=Estimating%20absolute%20rates%20of%20molecular%20evolution%20and%20divergence%20times:%20a%20penalized%20likelihood%20approach.&author=MJ%20Sanderson&volume=19&publication_year=2002&pages=101-109&pmid=11752195&doi=10.1093/oxfordjournals.molbev.a003974&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Sanderson2"> <span class="label">47.</span><cite>Sanderson MJ. Paloverde: an OpenGL 3-D phylogeny browser. Bioinf. 2006;22:1004–1006. doi: 10.1093/bioinformatics/btl044.</cite> [<a href="https://doi.org/10.1093/bioinformatics/btl044" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/16500938/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Bioinf&title=Paloverde:%20an%20OpenGL%203-D%20phylogeny%20browser.&author=MJ%20Sanderson&volume=22&publication_year=2006&pages=1004-1006&pmid=16500938&doi=10.1093/bioinformatics/btl044&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Kembel1"> <span class="label">48.</span><cite>Kembel SW, Ackerly DD, Blomberg SP, Cornwell WK, Cowan PD, et al. Picante: R tools for integrating phylogenies and ecology. 2009. R package version 0.7-2 Available: <a href="http://picante.r-forge.r-project.org" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">http://picante.r-forge.r-project.org</a>. Accessed 2011, Jan. 11.</cite> [<a href="https://doi.org/10.1093/bioinformatics/btq166" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/20395285/" class="usa-link">PubMed</a>]</li> <li id="pone.0031781-R1"> <span class="label">49.</span><cite>R Development Core Team. R: A language and environment for statistical computing. 2009. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL <a href="http://www.R-project.org/" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">http://www.R-project.org/</a>. Accessed 2011, Jan. 11.</cite> </li> <li id="pone.0031781-Blomberg1"> <span class="label">50.</span><cite>Blomberg SP, Garland TJ, Ives AR. Testing for phylogenetic signal in comparative data: behavioral traits are more labile. Evol. 2003;57:717–745. doi: 10.1111/j.0014-3820.2003.tb00285.x.</cite> [<a href="https://doi.org/10.1111/j.0014-3820.2003.tb00285.x" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">DOI</a>] [<a href="https://pubmed.ncbi.nlm.nih.gov/12778543/" class="usa-link">PubMed</a>] [<a href="https://scholar.google.com/scholar_lookup?journal=Evol&title=Testing%20for%20phylogenetic%20signal%20in%20comparative%20data:%20behavioral%20traits%20are%20more%20labile.&author=SP%20Blomberg&author=TJ%20Garland&author=AR%20Ives&volume=57&publication_year=2003&pages=717-745&pmid=12778543&doi=10.1111/j.0014-3820.2003.tb00285.x&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Maddison2"> <span class="label">51.</span><cite>Maddison WP, Maddison DR. Mesquite: a modular system for evolutionary analysis. 2008. Version 2.5, URL <a href="http://mesquiteproject.org" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">http://mesquiteproject.org</a>. Accessed 2009, May 05.</cite> </li> <li id="pone.0031781-Webb2"> <span class="label">52.</span><cite>Webb GJW, Messel H. analysis of Crocodylus porosus from the north coast of Arnhem Land, northern Australia. Aust J Zool. 1978;26:1–27.</cite> [<a href="https://scholar.google.com/scholar_lookup?journal=Aust%20J%20Zool&title=analysis%20of%20Crocodylus%20porosus%20from%20the%20north%20coast%20of%20Arnhem%20Land,%20northern%20Australia.&author=GJW%20Webb&author=H%20Messel&volume=26&publication_year=1978&pages=1-27&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> <li id="pone.0031781-Wermuth1"> <span class="label">53.</span><cite>Wermuth H, Fuchs K. Bestimmen von Kro-kodilen und ihrer Haute. New York: Gustav Fischer-Verlag; 1978. </cite> [<a href="https://scholar.google.com/scholar_lookup?title=Bestimmen%20von%20Kro-kodilen%20und%20ihrer%20Haute&author=H%20Wermuth&author=K%20Fuchs&publication_year=1978&" class="usa-link usa-link--external" data-ga-action="click_feat_suppl" target="_blank" rel="noopener noreferrer">Google Scholar</a>]</li> </ul></section></section></section><footer class="p courtesy-note font-secondary font-sm text-center"><hr class="headless"> <p>Articles from PLoS ONE are provided here courtesy of <strong>PLOS</strong></p></footer></section></article> </main> </div> </div> </div>  <div class="pmc-sidenav desktop:grid-col-4 display-flex"> <section class="pmc-sidenav__container" aria-label="Article resources and navigation"> <button type="button" class="usa-button pmc-sidenav__container__close usa-button--unstyled"> <img src="/static/img/usa-icons/close.svg" role="img" alt="Close" /> </button> <div class="display-none desktop:display-block"> <section class="margin-top-4 desktop:margin-top-0"> <h2 class="margin-top-0">ACTIONS</h2> <ul class="usa-list usa-list--unstyled usa-list--actions"> <li> <a href="https://doi.org/10.1371/journal.pone.0031781" class="usa-button usa-button--outline width-24 font-xs usa-link--external padding-left-0 padding-right-0" target="_blank" rel="noreferrer noopener" data-ga-category="actions" data-ga-action="click" data-ga-label="publisher_link_desktop" > <span class="height-3 display-inline-flex flex-align-center">View on publisher site</span> </a> </li> <li> <a href="pdf/pone.0031781.pdf" class="usa-button usa-button--outline width-24 display-inline-flex flex-align-center flex-justify-start padding-left-1" data-ga-category="actions" data-ga-action="click" data-ga-label="pdf_download_desktop" > <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/sprite.svg#file_download"></use> </svg> <span class="display-inline-flex flex-justify-center flex-1">PDF (572.5 KB)</span> </a> </li> <li> <button role="button" class="usa-button width-24 citation-dialog-trigger display-inline-flex flex-align-center flex-justify-start padding-left-1" aria-label="Open dialog with citation text in different styles" data-ga-category="actions" data-ga-action="open" data-ga-label="cite_desktop" data-all-citations-url="/resources/citations/3303775/" data-citation-style="nlm" data-download-format-link="/resources/citations/3303775/export/" > <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/sprite.svg#format_quote"></use> </svg> <span class="display-inline-flex flex-justify-center flex-1 button-label">Cite</span> </button> </li> <li> <button class="usa-button width-24 collections-dialog-trigger collections-button display-inline-flex flex-align-center flex-justify-start padding-left-1 collections-button-empty" aria-label="Save article in MyNCBI collections." data-ga-category="actions" data-ga-action="click" data-ga-label="collections_button_desktop" data-collections-open-dialog-enabled="false" data-collections-open-dialog-url="https://account.ncbi.nlm.nih.gov/?back_url=https%3A%2F%2Fpmc.ncbi.nlm.nih.gov%2Farticles%2FPMC3303775%2F%23open-collections-dialog" data-in-collections="false"> <svg class="usa-icon width-3 height-3 usa-icon--bookmark-full" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/action-bookmark-full.svg#icon"></use> </svg> <svg class="usa-icon width-3 height-3 usa-icon--bookmark-empty" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/action-bookmark-empty.svg#icon"></use> </svg> <span class="display-inline-flex flex-justify-center flex-1">Collections</span> </button> </li> <li class="pmc-permalink"> <button type="button" class="usa-button usa-button--outline width-24 display-inline-flex flex-align-center flex-justify padding-left-1 shadow-none" aria-label="Show article permalink" aria-expanded="false" aria-haspopup="true" data-ga-category="actions" data-ga-action="open" data-ga-label="permalink_desktop" > <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img" hidden> <use xlink:href="/static/img/sprite.svg#share"></use> </svg> <span class="display-inline-flex flex-justify-center flex-1 button-label">Permalink</span> </button> <div class="pmc-permalink__dropdown" hidden> <div class="pmc-permalink__dropdown__container"> <h2 class="usa-modal__heading margin-top-0 margin-bottom-2">PERMALINK</h2> <div class="pmc-permalink__dropdown__content"> <input type="text" class="usa-input" value="https://pmc.ncbi.nlm.nih.gov/articles/PMC3303775/" aria-label="Article permalink"> <button class="usa-button display-inline-flex pmc-permalink__dropdown__copy__btn margin-right-0" title="Copy article permalink" data-ga-category="save_share" data-ga-action="link" data-ga-label="copy_link"> <svg class="usa-icon" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#content_copy"></use> </svg> <span class="margin-left-1">Copy</span> </button> </div> </div> </div> </li> </ul> </section> </div> <section class="pmc-resources margin-top-6 desktop:margin-top-4" data-page-path="/articles/PMC3303775/"> <h2 class="margin-top-0">RESOURCES</h2> <div class="usa-accordion usa-accordion--multiselectable" data-allow-multiple> <h3 class="usa-accordion__heading"> <button type="button" class="usa-accordion__button" aria-expanded="false" aria-controls="resources-similar-articles" data-ga-category="resources_accordion" data-ga-action="open_similar_articles" data-ga-label="/articles/PMC3303775/" data-action-open="open_similar_articles" data-action-close="close_similar_articles" > Similar articles </button> </h3> <div id="resources-similar-articles" class="usa-accordion__content usa-prose" data-source-url="/resources/similar-article-links/22431965/" > </div> <h3 class="usa-accordion__heading"> <button type="button" class="usa-accordion__button" aria-expanded="false" aria-controls="resources-cited-by-other-articles" data-ga-category="resources_accordion" data-ga-action="open_cited_by" data-ga-label="/articles/PMC3303775/" data-action-open="open_cited_by" data-action-close="close_cited_by" > Cited by other articles </button> </h3> <div id="resources-cited-by-other-articles" class="usa-accordion__content usa-prose" data-source-url="/resources/cited-by-links/22431965/" > </div> <h3 class="usa-accordion__heading"> <button type="button" class="usa-accordion__button" aria-expanded="false" aria-controls="resources-links-to-ncbi-databases" data-ga-category="resources_accordion" data-ga-action="open_NCBI_links" data-ga-label="/articles/PMC3303775/" data-action-open="open_NCBI_links" data-action-close="close_NCBI_link" > Links to NCBI Databases </button> </h3> <div id="resources-links-to-ncbi-databases" class="usa-accordion__content usa-prose" data-source-url="/resources/db-links/3303775/" > </div> </div> </section> <section class="usa-in-page-nav usa-in-page-nav--wide margin-top-6 desktop:margin-top-4" data-title-text="On this page" data-title-heading-level="h2" data-scroll-offset="0" data-root-margin="-10% 0px -80% 0px" data-main-content-selector="main" data-threshold="1" hidden ></section> </section> </div> <div class="overlay" role="dialog" aria-label="Citation Dialog" hidden> <div class="dialog citation-dialog" aria-hidden="true"> <div class="display-inline-flex flex-align-center flex-justify width-full margin-bottom-2"> <h2 class="usa-modal__heading margin-0">Cite</h2> <button type="button" class="usa-button usa-button--unstyled close-overlay text-black width-auto" tabindex="1"> <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#close"></use> </svg> </button> </div> <div class="citation-text-block"> <div class="citation-text margin-bottom-2"></div> <ul class="usa-list usa-list--unstyled display-inline-flex flex-justify width-full flex-align-center"> <li> <button class="usa-button usa-button--unstyled text-no-underline display-flex flex-align-center copy-button dialog-focus" data-ga-category="save_share" data-ga-action="cite" data-ga-label="copy" tabindex="2"> <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#content_copy"></use> </svg> <span>Copy</span> </button> </li> <li> <a href="#" role="button" class="usa-button usa-button--unstyled text-no-underline display-flex flex-align-center export-button" data-ga-category="save_share" data-ga-action="cite" data-ga-label="download" title="Download a file for external citation management software" tabindex="3"> <svg class="usa-icon width-3 height-3" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#file_download"></use> </svg> <span class="display-none mobile-lg:display-inline">Download .nbib</span> <span class="display-inline mobile-lg:display-none">.nbib</span> </a> </li> <li> <div class="display-inline-flex flex-align-center"> <label class="usa-label margin-top-0">Format:</label> <select aria-label="Format" class="usa-select citation-style-selector padding-1 margin-top-0 border-0 padding-right-4" tabindex="4" > <option data-style-url-name="ama" value="AMA" > AMA </option> <option data-style-url-name="apa" value="APA" > APA </option> <option data-style-url-name="mla" value="MLA" > MLA </option> <option data-style-url-name="nlm" value="NLM" selected="selected"> NLM </option> </select> </div> </li> </ul> </div> </div> </div> <div class="overlay" role="dialog" hidden> <div id="collections-action-dialog" class="dialog collections-dialog" aria-hidden="true"> <div class="display-inline-flex flex-align-center flex-justify width-full margin-bottom-2"> <h2 class="usa-modal__heading margin-0">Add to Collections</h2> </div> <div class="collections-action-panel action-panel"> <form id="collections-action-dialog-form" class="usa-form maxw-full collections-action-panel-form action-panel-content action-form action-panel-smaller-selectors" data-existing-collections-url="/list-existing-collections/" data-add-to-existing-collection-url="/add-to-existing-collection/" data-create-and-add-to-new-collection-url="/create-and-add-to-new-collection/" data-myncbi-max-collection-name-length="100" data-collections-root-url="https://www.ncbi.nlm.nih.gov/myncbi/collections/"> <input type="hidden" name="csrfmiddlewaretoken" value="9eULSPyQVtqy60xL7wD9QLTM6VyehksiW9MJoMOBr1MaV0TJqPlM7yITWMKrPZ8c"> <fieldset class="usa-fieldset margin-bottom-2"> <div class="usa-radio"> <input type="radio" id="collections-action-dialog-new" class="usa-radio__input usa-radio__input--tile collections-new margin-top-0" name="collections" value="new" data-ga-category="collections_button" data-ga-action="click" data-ga-label="collections_radio_new" /> <label class="usa-radio__label" for="collections-action-dialog-new">Create a new collection</label> </div> <div class="usa-radio"> <input type="radio" id="collections-action-dialog-existing" class="usa-radio__input usa-radio__input--tile collections-existing" name="collections" value="existing" checked="true" data-ga-category="collections_button" data-ga-action="click" data-ga-label="collections_radio_existing" /> <label class="usa-radio__label" for="collections-action-dialog-existing">Add to an existing collection</label> </div> </fieldset> <fieldset class="usa-fieldset margin-bottom-2"> <div class="action-panel-control-wrap new-collections-controls"> <label for="collections-action-dialog-add-to-new" class="usa-label margin-top-0"> Name your collection <abbr title="required" class="usa-hint usa-hint--required text-no-underline">*</abbr> </label> <input type="text" name="add-to-new-collection" id="collections-action-dialog-add-to-new" class="usa-input collections-action-add-to-new" pattern="[^"&=<>/]*" title="The following characters are not allowed in the Name field: "&=<>/" maxlength="" data-ga-category="collections_button" data-ga-action="create_collection" data-ga-label="non_favorties_collection" required /> </div> <div class="action-panel-control-wrap existing-collections-controls"> <label for="collections-action-dialog-add-to-existing" class="usa-label margin-top-0"> Choose a collection </label> <select id="collections-action-dialog-add-to-existing" class="usa-select collections-action-add-to-existing" data-ga-category="collections_button" data-ga-action="select_collection" data-ga-label="($('.collections-action-add-to-existing').val() === 'Favorites') ? 'Favorites' : 'non_favorites_collection'"> </select> <div class="collections-retry-load-on-error usa-input-error-message selection-validation-message"> Unable to load your collection due to an error<br> <a href="#">Please try again</a> </div> </div> </fieldset> <div class="display-inline-flex"> <button class="usa-button margin-top-0 action-panel-submit" type="submit" data-loading-label="Adding..." data-pinger-ignore data-ga-category="collections_button" data-ga-action="click" data-ga-label="add"> Add </button> <button class="usa-button usa-button--outline margin-top-0 action-panel-cancel" aria-label="Close 'Add to Collections' panel" ref="linksrc=close_collections_panel" data-ga-category="collections_button" data-ga-action="click" data-ga-label="cancel"> Cancel </button> </div> </form> </div> </div> </div> </div> </div> </div> <footer class="ncbi-footer ncbi-dark-background " > <div class="ncbi-footer__icon-section"> <div class="ncbi-footer__social-header"> Follow NCBI </div> <div class="grid-container ncbi-footer__ncbi-social-icons-container"> <a href="https://twitter.com/ncbi" class="ncbi-footer__social-icon ncbi-footer__social-icon--gray" target="_blank" rel="noreferrer noopener"> <svg width="40" height="40" viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="m6.067 8 10.81 13.9L6 33.2h4.2l8.4-9.1 7.068 9.1H34L22.8 18.5 31.9 8h-3.5l-7.7 8.4L14.401 8H6.067Zm3.6 1.734h3.266l16.8 21.732H26.57L9.668 9.734Z"> </path> </svg> <span class="usa-sr-only">NCBI on X (formerly known as Twitter)</span> </a> <a href="https://www.facebook.com/ncbi.nlm" class="ncbi-footer__social-icon ncbi-footer__social-icon--gray" target="_blank" rel="noreferrer noopener"> <svg width="16" height="29" focusable="false" aria-hidden="true" viewBox="0 0 16 29" fill="none" xmlns="http://www.w3.org/2000/svg"> <path d="M3.8809 21.4002C3.8809 19.0932 3.8809 16.7876 3.8809 14.478C3.8809 14.2117 3.80103 14.1452 3.54278 14.1492C2.53372 14.1638 1.52334 14.1492 0.514288 14.1598C0.302626 14.1598 0.248047 14.0972 0.248047 13.8936C0.256034 12.4585 0.256034 11.0239 0.248047 9.58978C0.248047 9.37013 0.302626 9.30224 0.528931 9.3049C1.53798 9.31688 2.54837 9.3049 3.55742 9.31555C3.80103 9.31555 3.8809 9.26097 3.87957 9.00272C3.87158 8.00565 3.85428 7.00592 3.90753 6.00884C3.97142 4.83339 4.31487 3.73115 5.04437 2.78467C5.93095 1.63318 7.15699 1.09005 8.56141 0.967577C10.5582 0.79319 12.555 0.982221 14.5518 0.927641C14.7102 0.927641 14.7462 0.99287 14.7449 1.13664C14.7449 2.581 14.7449 4.02668 14.7449 5.47104C14.7449 5.67604 14.6517 5.68669 14.4946 5.68669C13.4523 5.68669 12.4113 5.68669 11.3703 5.68669C10.3506 5.68669 9.92057 6.10868 9.90593 7.13904C9.89661 7.7647 9.91525 8.39303 9.89794 9.01869C9.88995 9.26364 9.96583 9.31822 10.2015 9.31688C11.7204 9.30623 13.2393 9.31688 14.7595 9.3049C15.0257 9.3049 15.0723 9.3728 15.0444 9.62439C14.89 10.9849 14.7515 12.3467 14.6144 13.7085C14.5691 14.1571 14.5785 14.1585 14.1458 14.1585C12.8386 14.1585 11.5313 14.1665 10.2254 14.1518C9.95119 14.1518 9.89794 14.2317 9.89794 14.4899C9.90593 19.0799 9.89794 23.6752 9.91125 28.2612C9.91125 28.5674 9.8407 28.646 9.53186 28.6433C7.77866 28.6273 6.02414 28.6366 4.27094 28.634C3.82499 28.634 3.87158 28.6992 3.87158 28.22C3.87602 25.9472 3.87913 23.6739 3.8809 21.4002Z"> </path> </svg> <span class="usa-sr-only">NCBI on Facebook</span> </a> <a href="https://www.linkedin.com/company/ncbinlm" class="ncbi-footer__social-icon ncbi-footer__social-icon--gray" target="_blank" rel="noreferrer noopener"> <svg width="25" height="23" viewBox="0 0 26 24" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="M14.6983 9.98423C15.6302 9.24808 16.5926 8.74754 17.6762 8.51991C19.673 8.09126 21.554 8.30824 23.1262 9.7526C24.2351 10.7723 24.7529 12.1115 25.0165 13.5612C25.1486 14.3363 25.2105 15.1218 25.2015 15.9081C25.2015 18.3043 25.2015 20.6898 25.2082 23.0806C25.2082 23.3468 25.1549 23.444 24.8621 23.4414C23.1297 23.4272 21.3992 23.4272 19.6704 23.4414C19.4041 23.4414 19.3429 23.3588 19.3442 23.1019C19.3535 20.5194 19.3442 17.9368 19.3442 15.3543C19.3442 14.0005 18.3258 12.9448 17.0266 12.9488C15.7273 12.9528 14.6983 14.0071 14.6983 15.361C14.6983 17.9328 14.6917 20.5047 14.6983 23.0753C14.6983 23.3708 14.6198 23.444 14.3296 23.4427C12.6185 23.4294 10.9079 23.4294 9.19779 23.4427C8.93155 23.4427 8.86099 23.3735 8.86232 23.1086C8.8783 19.7619 8.88628 16.4144 8.88628 13.066C8.88628 11.5688 8.87874 10.0708 8.86365 8.57182C8.86365 8.3575 8.90758 8.27896 9.14054 8.28029C10.9048 8.29094 12.6687 8.29094 14.4321 8.28029C14.6464 8.28029 14.6983 8.34818 14.6983 8.54653C14.6903 9.00047 14.6983 9.45441 14.6983 9.98423Z"> </path> <path d="M6.55316 15.8443C6.55316 18.2564 6.55316 20.6699 6.55316 23.082C6.55316 23.3629 6.48127 23.4388 6.19906 23.4374C4.47737 23.4241 2.75568 23.4241 1.03399 23.4374C0.767751 23.4374 0.69986 23.3629 0.701191 23.1006C0.709178 18.2648 0.709178 13.4281 0.701191 8.59053C0.701191 8.34026 0.765089 8.27237 1.01669 8.2737C2.74991 8.28435 4.48048 8.28435 6.20838 8.2737C6.47462 8.2737 6.5465 8.33627 6.54517 8.6065C6.54783 11.0186 6.55316 13.4308 6.55316 15.8443Z"> </path> <path d="M3.65878 0.243898C5.36804 0.243898 6.58743 1.45529 6.58743 3.1406C6.58743 4.75801 5.32145 5.95742 3.60819 5.96807C3.22177 5.97614 2.83768 5.90639 2.47877 5.76299C2.11985 5.61959 1.79344 5.40546 1.51897 5.13334C1.24449 4.86123 1.02755 4.53668 0.881058 4.17902C0.734563 3.82136 0.661505 3.43788 0.666231 3.05141C0.67555 1.42601 1.9362 0.242566 3.65878 0.243898Z"> </path> </svg> <span class="usa-sr-only">NCBI on LinkedIn</span> </a> <a href="https://github.com/ncbi" class="ncbi-footer__social-icon ncbi-footer__social-icon--gray" target="_blank" rel="noreferrer noopener"> <svg width="28" height="27" viewBox="0 0 28 28" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="M16.7228 20.6334C17.5057 20.5527 18.2786 20.3944 19.0301 20.1608C21.3108 19.4193 22.5822 17.8259 22.963 15.4909C23.1228 14.5112 23.1814 13.5287 22.9883 12.5437C22.8106 11.6423 22.4013 10.8028 21.8007 10.1076C21.7526 10.0605 21.7197 10 21.7064 9.934C21.6931 9.86799 21.7 9.79952 21.7262 9.73748C22.0856 8.6206 21.9711 7.51969 21.601 6.42677C21.582 6.3497 21.5345 6.2827 21.468 6.23923C21.4016 6.19577 21.3211 6.17906 21.2429 6.19248C20.7329 6.21649 20.2313 6.33051 19.7611 6.52928C19.1103 6.7908 18.4899 7.12198 17.9104 7.51703C17.84 7.56996 17.7581 7.60551 17.6713 7.62078C17.5846 7.63605 17.4954 7.6306 17.4112 7.60489C15.2596 7.05882 13.0054 7.06203 10.8554 7.61421C10.7806 7.63586 10.7018 7.63967 10.6253 7.62534C10.5487 7.611 10.4766 7.57892 10.4148 7.53167C9.64788 7.03247 8.85171 6.58918 7.96368 6.33359C7.65781 6.24338 7.34123 6.19458 7.02239 6.18849C6.94879 6.17986 6.87462 6.19893 6.81432 6.242C6.75402 6.28507 6.71191 6.34904 6.69621 6.42145C6.32342 7.51437 6.2209 8.61527 6.56307 9.73348C6.59635 9.84264 6.64694 9.93316 6.54177 10.0516C5.47666 11.2604 5.09988 12.6834 5.19574 14.2676C5.2663 15.4244 5.46201 16.5466 6.01454 17.5769C6.84399 19.1171 8.21664 19.9119 9.85158 20.3352C10.3938 20.4706 10.9444 20.5698 11.4998 20.632C11.5384 20.7492 11.4506 20.7798 11.408 20.8291C11.1734 21.1179 10.9894 21.4441 10.8634 21.7942C10.7622 22.0458 10.8315 22.4039 10.6065 22.5516C10.263 22.7766 9.83827 22.8485 9.42421 22.8871C8.17936 23.0056 7.26471 22.4877 6.6283 21.4348C6.25552 20.8184 5.76956 20.3325 5.08523 20.0663C4.76981 19.9325 4.42139 19.8967 4.08537 19.9638C3.7898 20.029 3.73788 20.1901 3.93891 20.4111C4.03639 20.5234 4.14989 20.6207 4.27575 20.6999C4.9796 21.1318 5.51717 21.7884 5.80152 22.5636C6.37002 23.9973 7.48039 24.5697 8.93825 24.6323C9.43741 24.6575 9.93768 24.615 10.4254 24.5058C10.5892 24.4672 10.6531 24.4872 10.6517 24.6762C10.6451 25.4936 10.6637 26.3123 10.6517 27.131C10.6517 27.6635 10.1684 27.9297 9.58663 27.7393C8.17396 27.2671 6.84977 26.5631 5.66838 25.656C2.59555 23.2891 0.720966 20.1861 0.217704 16.3376C-0.357453 11.9127 0.911353 8.00824 3.98551 4.73881C6.11909 2.42656 8.99932 0.939975 12.1203 0.540191C16.5351 -0.0601815 20.4347 1.14323 23.7232 4.16373C26.2449 6.47869 27.724 9.37672 28.1048 12.7726C28.5828 17.0325 27.3686 20.7945 24.4768 23.9827C22.9762 25.6323 21.0956 26.8908 18.9982 27.6488C18.8783 27.6927 18.7585 27.738 18.636 27.7726C18.0356 27.9404 17.6189 27.6395 17.6189 27.0098C17.6189 25.7452 17.6308 24.4806 17.6295 23.2159C17.6329 22.9506 17.6128 22.6856 17.5696 22.4238C17.4325 21.6664 17.3419 21.484 16.7228 20.6334Z"> </path> </svg> <span class="usa-sr-only">NCBI on GitHub</span> </a> <a href="https://ncbiinsights.ncbi.nlm.nih.gov/" class="ncbi-footer__social-icon ncbi-footer__social-icon--gray" target="_blank" rel="noreferrer noopener"> <svg width="26" height="26" viewBox="0 0 27 27" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="M23.7778 26.4574C23.1354 26.3913 22.0856 26.8024 21.636 26.3087C21.212 25.8444 21.4359 24.8111 21.324 24.0347C19.9933 14.8323 14.8727 8.80132 6.09057 5.85008C4.37689 5.28406 2.58381 4.99533 0.779072 4.99481C0.202773 4.99481 -0.0229751 4.83146 0.00455514 4.21479C0.0660406 3.08627 0.0660406 1.95525 0.00455514 0.826734C-0.0413285 0.0815827 0.259669 -0.0193618 0.896534 0.00266238C6.96236 0.222904 12.3693 2.24179 16.9889 6.16209C22.9794 11.2478 26.1271 17.7688 26.4372 25.648C26.4629 26.294 26.3179 26.5271 25.6609 26.4684C25.0827 26.417 24.4991 26.4574 23.7778 26.4574Z"> </path> <path d="M14.8265 26.441C14.0924 26.441 13.2371 26.6795 12.6626 26.3786C12.0092 26.0372 12.3781 25.0644 12.246 24.378C11.1154 18.5324 6.6849 14.5497 0.74755 14.1001C0.217135 14.0615 -0.0104482 13.9422 0.0134113 13.3659C0.0519536 12.1454 0.0482829 10.9213 0.0134113 9.69524C-0.00127145 9.14464 0.196946 9.03268 0.703502 9.04736C9.21217 9.27128 16.5994 16.2511 17.2804 24.7231C17.418 26.4446 17.418 26.4446 15.6579 26.4446H14.832L14.8265 26.441Z"> </path> <path d="M3.58928 26.4555C2.64447 26.4618 1.73584 26.0925 1.06329 25.4289C0.39073 24.7653 0.00933763 23.8617 0.0030097 22.9169C-0.00331824 21.9721 0.365937 21.0635 1.02954 20.3909C1.69315 19.7184 2.59675 19.337 3.54156 19.3306C4.48637 19.3243 5.39499 19.6936 6.06755 20.3572C6.7401 21.0208 7.1215 21.9244 7.12782 22.8692C7.13415 23.814 6.7649 24.7226 6.10129 25.3952C5.43768 26.0677 4.53409 26.4491 3.58928 26.4555Z"> </path> </svg> <span class="usa-sr-only">NCBI RSS feed</span> </a> </div> </div> <div data-testid="gridContainer" class="grid-container ncbi-footer__container"> <div class="grid-row ncbi-footer__main-content-container" data-testid="grid"> <div class="ncbi-footer__column"> <p class="ncbi-footer__circled-icons-heading"> Connect with NLM </p> <div class="ncbi-footer__circled-icons-list"> <a href=https://twitter.com/nlm_nih class="ncbi-footer__social-icon ncbi-footer__social-icon--circled" target="_blank" rel="noreferrer noopener"> <svg width="32" height="32" viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="m6.067 8 10.81 13.9L6 33.2h4.2l8.4-9.1 7.068 9.1H34L22.8 18.5 31.9 8h-3.5l-7.7 8.4L14.401 8H6.067Zm3.6 1.734h3.266l16.8 21.732H26.57L9.668 9.734Z"> </path> </svg> <span class="usa-sr-only">NLM on X (formerly known as Twitter)</span> </a> <a href=https://www.facebook.com/nationallibraryofmedicine class="ncbi-footer__social-icon ncbi-footer__social-icon--circled" target="_blank" rel="noreferrer noopener"> <svg width="13" height="24" viewBox="0 0 13 24" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="M4.11371 23.1369C4.11371 23.082 4.11371 23.0294 4.11371 22.9745V12.9411H0.817305C0.6709 12.9411 0.670898 12.9411 0.670898 12.8016C0.670898 11.564 0.670898 10.3287 0.670898 9.09341C0.670898 8.97903 0.705213 8.95158 0.815017 8.95158C1.8673 8.95158 2.91959 8.95158 3.97417 8.95158H4.12057V8.83263C4.12057 7.8055 4.12057 6.7738 4.12057 5.74897C4.1264 4.92595 4.31387 4.11437 4.66959 3.37217C5.12916 2.38246 5.94651 1.60353 6.95717 1.1921C7.64827 0.905008 8.3913 0.764035 9.13953 0.778051C10.0019 0.791777 10.8644 0.830666 11.7268 0.860404C11.8869 0.860404 12.047 0.894717 12.2072 0.90158C12.2964 0.90158 12.3261 0.940469 12.3261 1.02968C12.3261 1.5421 12.3261 2.05452 12.3261 2.56465C12.3261 3.16857 12.3261 3.7725 12.3261 4.37642C12.3261 4.48165 12.2964 4.51367 12.1912 4.51138C11.5369 4.51138 10.8804 4.51138 10.2261 4.51138C9.92772 4.51814 9.63058 4.5526 9.33855 4.61433C9.08125 4.6617 8.84537 4.78881 8.66431 4.97766C8.48326 5.16652 8.3662 5.40755 8.32972 5.66661C8.28476 5.89271 8.26027 6.1224 8.25652 6.35289C8.25652 7.19014 8.25652 8.02969 8.25652 8.86923C8.25652 8.89439 8.25652 8.91955 8.25652 8.95615H12.0219C12.1797 8.95615 12.182 8.95616 12.1614 9.10714C12.0768 9.76596 11.9876 10.4248 11.9029 11.0813C11.8312 11.6319 11.7626 12.1824 11.697 12.733C11.6719 12.9434 11.6787 12.9434 11.4683 12.9434H8.26338V22.899C8.26338 22.979 8.26338 23.0591 8.26338 23.1392L4.11371 23.1369Z"> </path> </svg> <span class="usa-sr-only">NLM on Facebook</span> </a> <a href=https://www.youtube.com/user/NLMNIH class="ncbi-footer__social-icon ncbi-footer__social-icon--circled" target="_blank" rel="noreferrer noopener"> <svg width="21" height="15" viewBox="0 0 21 15" fill="none" xmlns="http://www.w3.org/2000/svg" focusable="false" aria-hidden="true"> <path d="M19.2561 1.47914C18.9016 1.15888 18.5699 0.957569 17.2271 0.834039C15.5503 0.678484 13.2787 0.655608 11.563 0.65332H9.43556C7.71987 0.65332 5.4483 0.678484 3.77151 0.834039C2.43098 0.957569 2.097 1.15888 1.74242 1.47914C0.813665 2.32097 0.619221 4.62685 0.598633 6.89384C0.598633 7.31781 0.598633 7.74101 0.598633 8.16345C0.626084 10.4121 0.827391 12.686 1.74242 13.521C2.097 13.8412 2.4287 14.0425 3.77151 14.1661C5.4483 14.3216 7.71987 14.3445 9.43556 14.3468H11.563C13.2787 14.3468 15.5503 14.3216 17.2271 14.1661C18.5676 14.0425 18.9016 13.8412 19.2561 13.521C20.1712 12.6929 20.3725 10.451 20.3999 8.22064C20.3999 7.74025 20.3999 7.25986 20.3999 6.77946C20.3725 4.54907 20.1689 2.30724 19.2561 1.47914ZM8.55942 10.5311V4.65201L13.5601 7.50005L8.55942 10.5311Z" fill="white" /> </svg> <span class="usa-sr-only">NLM on YouTube</span> </a> </div> </div> <address class="ncbi-footer__address ncbi-footer__column"> <p> <a class="usa-link usa-link--external" href="https://www.google.com/maps/place/8600+Rockville+Pike,+Bethesda,+MD+20894/%4038.9959508, -77.101021,17z/data%3D!3m1!4b1!4m5!3m4!1s0x89b7c95e25765ddb%3A0x19156f88b27635b8!8m2!3d38.9959508! 4d-77.0988323" rel="noopener noreferrer" target="_blank">National Library of Medicine <br/> 8600 Rockville Pike<br/> Bethesda, MD 20894</a> </p> </address> <ul class="usa-list usa-list--unstyled ncbi-footer__vertical-list ncbi-footer__column"> <li class="ncbi-footer__vertical-list-item"> <a href="https://www.nlm.nih.gov/web_policies.html" class="usa-link usa-link--alt ncbi-footer__link" > Web Policies </a> </li> <li class="ncbi-footer__vertical-list-item"> <a href="https://www.nih.gov/institutes-nih/nih-office-director/office-communications-public-liaison/freedom-information-act-office" class="usa-link usa-link--alt ncbi-footer__link" > FOIA </a> </li> <li class="ncbi-footer__vertical-list-item"> <a href="https://www.hhs.gov/vulnerability-disclosure-policy/index.html" class="usa-link usa-link--external usa-link--alt ncbi-footer__link" rel="noreferrer noopener" target='_blank' > HHS Vulnerability Disclosure </a> </li> </ul> <ul class="usa-list usa-list--unstyled ncbi-footer__vertical-list ncbi-footer__column"> <li class="ncbi-footer__vertical-list-item"> <a href="https://support.nlm.nih.gov/" class="usa-link usa-link--alt ncbi-footer__link" > Help </a> </li> <li class="ncbi-footer__vertical-list-item"> <a href="https://www.nlm.nih.gov/accessibility.html" class="usa-link usa-link--alt ncbi-footer__link" > Accessibility </a> </li> <li class="ncbi-footer__vertical-list-item"> <a href="https://www.nlm.nih.gov/careers/careers.html" class="usa-link usa-link--alt ncbi-footer__link" > Careers </a> </li> </ul> </div> <div class="grid-row grid-col-12" data-testid="grid"> <ul class="ncbi-footer__bottom-links-list"> <li class="ncbi-footer__bottom-list-item"> <a href="https://www.nlm.nih.gov/" class="usa-link usa-link--alt ncbi-footer__link" > NLM </a> </li> <li class="ncbi-footer__bottom-list-item"> <a href="https://www.nih.gov/" class="usa-link usa-link--alt ncbi-footer__link" > NIH </a> </li> <li class="ncbi-footer__bottom-list-item"> <a href="https://www.hhs.gov/" class="usa-link usa-link--external usa-link--alt ncbi-footer__link" rel="noreferrer noopener" target='_blank' > HHS </a> </li> <li class="ncbi-footer__bottom-list-item"> <a href="https://www.usa.gov/" class="usa-link usa-link--external usa-link--alt ncbi-footer__link" rel="noreferrer noopener" target='_blank' > USA.gov </a> </li> </ul> </div> </div> </footer> <script type="text/javascript" src="https://cdn.ncbi.nlm.nih.gov/core/pinger/pinger.js"> </script> <button class="back-to-top" data-ga-category="pagination" data-ga-action="back_to_top"> <label>Back to Top</label> <svg class="usa-icon order-0" aria-hidden="true" focusable="false" role="img"> <use xlink:href="/static/img/sprite.svg#arrow_upward"></use> </svg> </button> <script src="https://code.jquery.com/jquery-3.5.0.min.js" integrity="sha256-xNzN2a4ltkB44Mc/Jz3pT4iU1cmeR0FkXs4pru/JxaQ=" crossorigin="anonymous"> </script> <script type="text/javascript">var exports = {};</script> <script src="/static/CACHE/js/output.13b077bc3ffd.js"></script> <script type="application/javascript"> window.ncbi = window.ncbi || {}; window.ncbi.pmc = window.ncbi.pmc || {}; window.ncbi.pmc.options = { logLevel: 'INFO', staticEndpoint: '/static/', citeCookieName: 'pmc-cf', }; </script> <script type="module" crossorigin="" src="/static/assets/base-9bea7450.js"></script> <script type="module" crossorigin="" src="/static/assets/article-722d91a2.js"></script> </body> </html>

CINXE.COM

Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation - PMC