The Skeleton of the Manus of Scelidotherium (Xenarthra, Mylodontidae) Specimens from the Pleistocene of the Province of Córdoba, Argentina, and its Systematic Implications

Abstract

Dental and craniomandibular data have been predominantly used to infer relationships among mylodontid ground sloths. Recent studies indicate the osteology of the manus also provides useful data to test phylogenetic relationships in mylodontine mylodontids. Here we provide new comparative data from the study of the manus of a member of the Scelidotheriinae, Scelidotherium Owen, 1839, based on specimens from the Province of Córdoba that provide information on the variation and systematic relationships of the genus. The Scelidotherium material from the Province of Córdoba in central Argentina presents several morphological differences with material of the genus from northwestern Argentina. The manus of Scelidotherium shares several traits with Catonyx Ameghino, 1891, but not with Valgipes Gervais, 1874. These include: trapezoid with a sharp ridge on the articular surface for metacarpal II; magnum with at least half of articular surface for metacarpal II located on the dorsal half of the medial and distal aspects of the bone; metacarpal II with a notch on the axial border of its distal articular surface; and ungual process of the distal phalanx of the second digit markedly dorsopalmarly flattened. A phylogenetic analysis that includes osteological characters of the manus indicates that within the family Scelidotheriinae, Scelidotherium is more closely related to Catonyx than to Valgipes or Proscelidodon gracillimus Rovereto, 1914.