{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,13]],"date-time":"2026-05-13T08:06:27Z","timestamp":1778659587999,"version":"3.51.4"},"reference-count":100,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2025,10,2]],"date-time":"2025-10-02T00:00:00Z","timestamp":1759363200000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"ANID PCHA\/Becas Chile","award":["2016-72170286"],"award-info":[{"award-number":["2016-72170286"]}]},{"DOI":"10.13039\/100006271","name":"National Museum of Natural History, Smithsonian Institution","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100006271","id-type":"DOI","asserted-by":"crossref"}]},{"name":"National Science Foundation Earth Sciences Postdoctoral Fellowship","award":["#1249920"],"award-info":[{"award-number":["#1249920"]}]},{"name":"NMNH Small Grant Award"},{"name":"NMNH Office of the Director"},{"name":"Smithsonian Institution\u2019s Remington Kellogg Fund"},{"name":"National Geographic Society Committee on Research Exploration","award":["8903-11, 9019-11"],"award-info":[{"award-number":["8903-11, 9019-11"]}]},{"name":"U-REDES"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>The evolution of marine mammals in South America includes unique and extinct lineages found nowhere else in the world, such as the walrus-convergent whale <jats:italic>Odobenocetops<\/jats:italic> and multiple aquatic sloth species belonging to the genus <jats:italic>Thalassocnus<\/jats:italic>. Aquatic sloths have been collected from Mio-Pliocene marine deposits in Peru and Chile, and terrestrial deposits in Argentina. In Chile, these occurrences range over 800 km across several basins from the Bah\u00eda Inglesa, Coquimbo, and Horc\u00f3n formations. Here we report aquatic sloth material belonging to the species <jats:italic>Thalassocnus natans<\/jats:italic> from a new locality, Norte Bah\u00eda Caldera from the Bah\u00eda Inglesa Formation in the Atacama Region. We find multiple lines of evidence to support a late Miocene age for this material, which consists of a nearly complete skeleton, including cranial and postcranial remains and associated mandible and postcranial elements that represent the most complete <jats:italic>Thalassocnus<\/jats:italic> specimens reported yet from Chile. Based on this finding, we review the stratigraphic origin and geologic age of <jats:italic>Thalassocnus<\/jats:italic> species from the western coast of South America and determine that remains from the Upper Pliocene of central Chile represent the youngest known record of this genus to date. Our review also suggests that overlapping stratigraphic ranges for type material of <jats:italic>T. antiquus<\/jats:italic> with both <jats:italic>T. natans<\/jats:italic> and <jats:italic>T. littoralis<\/jats:italic> weakens the proposed argument for <jats:italic>Thalassocnus<\/jats:italic> evolution through anagenesis succession. Finally, in the context of <jats:italic>Thalassocnus<\/jats:italic> material from Chile and Peru, including other marine mammal herbivores (<jats:italic>e.g<\/jats:italic>., sirenians), we demonstrate that one of the most unusual features of this guild is that South American marine mammal herbivores did not reach the body sizes of their analogous counterparts (<jats:italic>i.e<\/jats:italic>., desmostylians and sirenians) in the North Pacific. This observation builds on other paleontological evidence about the unusual features of the Peruvian biotic province during the Neogene.<\/jats:p>","DOI":"10.7717\/peerj.19897","type":"journal-article","created":{"date-parts":[[2025,10,2]],"date-time":"2025-10-02T08:00:21Z","timestamp":1759392021000},"page":"e19897","source":"Crossref","is-referenced-by-count":1,"title":["Aquatic sloths (<i>Thalassocnus<\/i>) from the Miocene of Chile and the evolution of marine mammal herbivory in the Pacific Ocean"],"prefix":"10.7717","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1497-364X","authenticated-orcid":true,"given":"Ana M.","family":"Valenzuela-Toro","sequence":"first","affiliation":[{"name":"\u00c1rea Cient\u00edfica, Centro de Investigaci\u00f3n y Avance de la Paleontolog\u00eda e Historia Natural de Atacama, CIAHN Atacama, Caldera, Chile"},{"name":"Department of Paleobiology, National Museum of Natural History Smithsonian Institution, Washington DC, Washington DC, United States"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4678-5782","authenticated-orcid":true,"given":"Nicholas D.","family":"Pyenson","sequence":"additional","affiliation":[{"name":"Department of Paleobiology, National Museum of Natural History Smithsonian Institution, Washington DC, Washington DC, United States"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0339-0556","authenticated-orcid":true,"given":"Jorge","family":"Velez-Juarbe","sequence":"additional","affiliation":[{"name":"Department of Mammalogy, Natural History Museum of Los Angeles County, Los Angeles, California, United States"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mario E.","family":"Su\u00e1rez","sequence":"additional","affiliation":[{"name":"Atacama F\u00f3sil Limitada, Caldera, Chile"},{"name":"Laboratorio de Ontogenia y Filogenia, Departamento de Biolog\u00eda, Facultad de Ciencias, Universidad de Chile, Santiago, Chile"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"4443","published-online":{"date-parts":[[2025,10,2]]},"reference":[{"issue":"2","key":"10.7717\/peerj.19897\/ref-1","doi-asserted-by":"publisher","first-page":"115","DOI":"10.7203\/sjp.21.2.20485","article-title":"Ping\u00fcinos (Aves, Spheniscidae) en Coquimbo (Mioceno medio-Plioceno tard\u00edo), Chile y su vinculaci\u00f3n con las corrientes oce\u00e1nicas","volume":"21","author":"Acosta-Hospitaleche","year":"2006","journal-title":"Spanish Journal of Palaeontology"},{"issue":"2","key":"10.7717\/peerj.19897\/ref-2","doi-asserted-by":"publisher","first-page":"169","DOI":"10.1007\/s10914-014-9268-3","article-title":"Osteology and functional morphology of the forelimb of the marine sloth Thalassocnus (Mammalia, Tardigrada)","volume":"22","author":"Amson","year":"2015a","journal-title":"Journal of Mammalian 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Nanosiren garciae, gen. et sp. nov. and Nanosiren sanchezi, sp. nov","volume":"28","author":"Domning","year":"2008","journal-title":"Journal of Vertebrate Paleontology"},{"issue":"4","key":"10.7717\/peerj.19897\/ref-31","doi-asserted-by":"publisher","first-page":"506","DOI":"10.1111\/j.1440-1738.1994.tb00129.x","article-title":"Summary of taxa and distribution of Sirenia in the North Pacific Ocean","volume":"3","author":"Domning","year":"1994","journal-title":"Island Arc"},{"issue":"4914","key":"10.7717\/peerj.19897\/ref-32","doi-asserted-by":"publisher","first-page":"170","DOI":"10.1126\/science.245.4914.170","article-title":"Magnification of secondary production by kelp detritus in coastal marine ecosystems","volume":"245","author":"Duggins","year":"1989","journal-title":"Science"},{"issue":"6","key":"10.7717\/peerj.19897\/ref-33","doi-asserted-by":"publisher","first-page":"1139","DOI":"10.1111\/j.1475-4983.2012.01201.x","article-title":"Origin of the white shark Carcharodon 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