Astrapotheres from Cañadón Vaca, middle Eocene of central Patagonia: New insights on diversity, anatomy, and early evolution of Astrapotheria

Abstract

Astrapotheria is one of the most emblematic groups of endemic South American ungulate-like extinct mammals, traditionally compared with modern tapirs and rhinos. Oldest astrapotheres are known from the early Eocene Itaboraian fauna (Brazil), but the earliest diverse astrapothere assemblage is known from the middle Eocene Cañadón Vaca Member of the Sarmiento Formation exposed at Cañadón Vaca (Vacan subage of the Casamayoran Land Mammal Age), in central Patagonia, Argentina. Previous reports of astrapotheres from Cañadón Vaca included Trigonostylops, Tetragonostylops, Albertogaudrya, and Scaglia, but only the record of the latter was unequivocal. New materials from Cañadón Vaca described herein confirms the occurrence of Trigonostylops (T. wortmani) and of Tetragonostylops (likely represented by a species different from the nominal species from Itaboraí). Additionally, two other taxa are identified: The former, described as cf. Scaglia cf. kraglievichorum, is represented by a partial skull with an unusual combination of cranial characters, and could correspond to an adult of Scaglia kraglievichorum (known by a juvenile skull); the other taxon is represented by a partial mandible with distinctive osteological and dental features, but the possibility of its belonging to Scaglia cannot be discarded. The occurrence of Albertogaudrya in Cañadón Vaca could not be confirmed by the examination of the new and previous collections. Astrapotheres from Cañadón Vaca show a wide morphological disparity of cranial designs, but all consistently share long, unreduced nasals, thus the presumed possession of a short tapir-like proboscis only typifies the post-Casamayoran astrapotheres.