{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T01:08:28Z","timestamp":1791248908281,"version":"4.1.0"},"reference-count":56,"publisher":"National Academy of Sciences","issue":"15","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2008,4,15]]},"abstract":"<jats:p>\n                    The order Proboscidea includes extant elephants and their extinct relatives and is closely related to the aquatic sirenians (manatees and dugongs) and terrestrial hyracoids (hyraxes). Some analyses of embryological, morphological, and paleontological data suggest that proboscideans and sirenians shared an aquatic or semiaquatic common ancestor, but independent tests of this hypothesis have proven elusive. Here we test the hypothesis of an aquatic ancestry for advanced proboscideans by measuring \u03b4\n                    <jats:sup>18<\/jats:sup>\n                    O in tooth enamel of two late Eocene proboscidean genera,\n                    <jats:italic>Barytherium<\/jats:italic>\n                    and\n                    <jats:italic>Moeritherium<\/jats:italic>\n                    , which are sister taxa of Oligocene-to-Recent proboscideans. The combination of low \u03b4\n                    <jats:sup>18<\/jats:sup>\n                    O values and low \u03b4\n                    <jats:sup>18<\/jats:sup>\n                    O standard deviations in\n                    <jats:italic>Barytherium<\/jats:italic>\n                    and\n                    <jats:italic>Moeritherium<\/jats:italic>\n                    matches the isotopic pattern seen in aquatic and semiaquatic mammals, and differs from that of terrestrial mammals. \u03b4\n                    <jats:sup>13<\/jats:sup>\n                    C values of these early proboscideans suggest that both genera are likely to have consumed freshwater plants, although a component of C\n                    <jats:sub>3<\/jats:sub>\n                    terrestrial vegetation cannot be ruled out. The simplest explanation for the combined evidence from isotopes, dental functional morphology, and depositional environments is that\n                    <jats:italic>Barytherium<\/jats:italic>\n                    and\n                    <jats:italic>Moeritherium<\/jats:italic>\n                    were at least semiaquatic and lived in freshwater swamp or riverine environments, where they grazed on freshwater vegetation. These results lend new support to the hypothesis that Oligocene-to-Recent proboscideans are derived from amphibious ancestors.\n                  <\/jats:p>","DOI":"10.1073\/pnas.0800884105","type":"journal-article","created":{"date-parts":[[2008,4,14]],"date-time":"2008-04-14T21:10:43Z","timestamp":1208207443000},"page":"5786-5791","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":54,"title":["Stable isotope evidence for an amphibious phase in early proboscidean evolution"],"prefix":"10.1073","volume":"105","author":[{"given":"Alexander G. S. C.","family":"Liu","sequence":"first","affiliation":[{"name":"*Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Erik R.","family":"Seiffert","sequence":"additional","affiliation":[{"name":"Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794-8081; and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elwyn L.","family":"Simons","sequence":"additional","affiliation":[{"name":"Division of Fossil Primates, Duke Lemur Center, 1013 Broad Street, Durham, NC 27705"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[2008,4,15]]},"reference":[{"key":"e_1_3_3_1_2","first-page":"239","article-title":"New data on Phosphatherium escuilliei (Mammalia, Proboscidea) from the early Eocene of Morocco, and its impact on the phylogeny of Proboscidea and lophodont ungulates (Translated from French)","volume":"27","author":"Gheerbrant E","year":"2005","unstructured":"E Gheerbrant, et al., New data on Phosphatherium escuilliei (Mammalia, Proboscidea) from the early Eocene of Morocco, and its impact on the phylogeny of Proboscidea and lophodont ungulates (Translated from French). 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