Bibliography and Index of the Sirenia and Desmostylia  

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"Argot, Christine"

Amson, Eli; de Muizon, Christian; Laurin, Michel; Argot, Christine; de Buffrénil, Vivian (detail)
Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru.
Proceedings of the Royal Society B 281(1782). DOI: 10.1098/rspb.2014.0192. March 12, 2014.
–ABSTRACT: Non-pathological densification (osteosclerosis) and swelling (pachyostosis) of bones are the main modifications affecting the skeleton of land vertebrates (tetrapods) that returned to water. However, a precise temporal calibration of the acquisition of such adaptations is still wanting. Here, we assess the timing of such acquisition using the aquatic sloth Thalassocnus, from the Neogene of the Pisco Formation, Peru. This genus is represented by five species occurring in successive vertebrate-bearing horizons of distinct ages. It yields the most detailed data about the gradual acquisition of aquatic adaptations among tetrapods, in displaying increasing osteosclerosis and pachyostosis through time. Such modifications, reflecting a shift in the habitat from terrestrial to aquatic, occurred over a short geological time span (ca 4 Myr). Otherwise, the bones of terrestrial pilosans (sloths and anteaters) are much more compact than the mean mammalian condition, which suggests that the osteosclerosis of Thalassocnus may represent an exaptation.
Amson, Eli; Argot, Christine; McDonald, H. Gregory; de Muizon, Christian (detail)
Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada).
Journal of Mammalian Evolution 22 (2):169-242. 30 tables. 47 tables. DOI: 10.1007/s10914-014-9268-3. June 2015.
–Abstract: 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.
Amson, Eli; Muizon, Christian de; Domning, Daryl Paul; Argot, Christine; Buffrénil, Vivian de (detail)
Bone histology as a clue for resolving the puzzle of a dugong rib in the Pisco Formation, Peru.
Journal of Vertebrate Paleontology 35(3): e922981 (4 pp.) 2 figs. DOI: 10.1080/02724634.2014.922981 May 2015 (publ. online Apr. 22, 2015).
–A supposedly dugongine rib described by Muizon & Domning (1985) and Domning & Aguilera (2008a) is reidentified as an aquatic sloth (Thalassocnus sp.).

Daryl P. Domning, Research Associate, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, and Laboratory of Evolutionary Biology, Department of Anatomy, College of Medicine, Howard University, Washington, D.C. 20059.
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