A new early species of the aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the Late Miocene of Peru

Christian De Muizon, H. Gregory McDonald, Rodolfo Salas, Mario Urbina

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Abstract

Thalassocnus antiquus, sp. nov., is a marine nothrothere from the late Miocene Aguada de Lomas vertebrate horizon (ca. 7 to 8 Ma) of the Pisco Formation in the Sacaco area of the southern coast of Peru. It is similar to the slightly younger latest Miocene Thalassocnus natans, but smaller and distinctly more gracile. The sloping morphology of the lateral border of the nares in T. antiquus differs from the probably plesiomorphic subvertical edge of the nares in T. natans. Parsimony analysis does not resolve the relative positions of T. antiquus and T. natans, and, therefore, does not fully confirm the possibility of a single Thalassocnus lineage, which spans over 4 Ma. However, Thalassocnus is an endemic genus and the stratigraphic distribution of its four species is well known. Furthermore, some characters indicate a continuous evolution from the oldest (T. antiquus) to the youngest species (T. carolomartini). Therefore, we prefer the hypothesis of a single Thalassocnus lineage, although a more complex evolutionary scenario is not discarded.
Original languageAmerican English
Pages (from-to)886-894
Number of pages9
JournalJournal of Vertebrate Paleontology
Volume23
Issue number4
DOIs
StatePublished - 1 Jan 2003

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