Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada)

Thalassocnus is a genus of “ground sloths” known from Neogene deposits, for the great majority of specimens, of the Pisco Formation (Peru). Five species are recognized, their description being currently restricted, for the most part, to the skull, mandible, and dentition. The bones of the forelimb a...

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Bibliographic Details
Published in:Journal of mammalian evolution 2015-06, Vol.22 (2), p.169-242
Main Authors: Amson, Eli, Argot, Christine, McDonald, H. Gregory, de Muizon, Christian
Format: Article
Language:English
Subjects:
Animal Genetics and Genomics
Anthropology
Biodiversity
Biomedical and Life Sciences
Dentition
Earth Sciences
Evolutionary Biology
Functional morphology
Human Genetics
Humerus
Life Sciences
Mammalia
Mandible
Neogene
Original Paper
Paleontology
Populations and Evolution
Rhizomes
Sciences of the Universe
Species
Tardigrada
Teeth
Thalassocnus
Ulna
Uprooting
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Summary:Thalassocnus is a genus of “ground sloths” known from Neogene deposits, for the great majority of specimens, of the Pisco Formation (Peru). Five species are recognized, their description being currently restricted, for the most part, to the skull, mandible, and dentition. The bones of the forelimb are here described, and compared among the species of Thalassocnus and to other pilosans. The main characteristics of the forelimb of Thalassocnus relative to other sloths are the shortness of the humerus and radius, and the specialized digits. Moreover, the late species of the genus are characterized by the development of the pronator ridge of the radius, stoutness of the ulna, widening of the proximal carpal row, and shortening of the metacarpals. Analogies with extant tetrapods are proposed in order to infer plausible aquatic functions of the forelimb of Thalassocnus . In addition to paddling, it is argued that the forelimb of Thalassocnus was involved in bottom-walking, a function similarly found in extant sirenians. However, the function of the forelimb of Thalassocnus differs drastically from that of the latter, since it was likely involved in an activity related to obtaining food such as uprooting seagrass rhizomes.
ISSN:1064-7554
1573-7055
DOI:10.1007/s10914-014-9268-3