Preliminary report of Deseadan sloths from Quebrada Fiera (Mendoza Province, Argentina)

PUJOS, F.; CARLINI, A.A.; CERDEÑO, E.; PRÁMPARO, M.B.

Neuquen (Argentina)

Congreso; Tercero Congreso Latinoamericano de Paleontología de Vertebrados; 2008

Deseadan SALMA (29-24,5 My) is a key period in South American mammal evolution, with the appearance of primates, the diversification of rodents and the establishing of sloths (Tardigrada). Sloths appear at least during the early Oligocene (McKenna et al., 2006) and begin to be abundant and diversified during the late Oligocene (Pujos & De Iuliis, 2007). The “Pyrotherium fauna” was identified by Ameghino (1895) in the La Flecha site (Santa Cruz Province) and defined as Deseadan SALMA by Pascual et al. (1965). Traditional Deseadan localities are situated in Patagonia (e.g., La Flecha and Cabeza Blanca) and the Bolivian Altiplano (Salla and Lacayani). Recently, new Deseadan localities have been identified in Uruguay and Argentina (Fray Bentos) and Peru (Moquegua). Currently, four sloth clades are generally recognized: Mylodontidae, Megatheriidae, Megalonychidae, and Nothrotheriidae. Later Engelmann (1987) described Pseudoglyptodon from Salla, a sloth with glyptodontoid teeth. More recently, Carlini & Scillato-Yané (2004) and Pujos & De Iuliis (2007) described some megalonychid and mylodontoid (Orophodontidae) sloths from La Flecha and Salla, respectively. The fauna from Quebrada Fiera in Mendoza Province (central-western Argentina) was noted by Gorroño et al. (1979) and listed by Pascual and de la Fuente (1993). Recent paleontological campaigns lead by A.A.C. (1996), M.B.P. and E.C. (2006-2008) recovered several remains of basal sloths and Cingulata. Among them, Mylodontoid sloths are the most abundant, and the most complete remain is a humerus. This specimen is short, massive, anteroposteriorly compressed with a strong medial epicondyle and an entepicondylar crest. The tubercles are huge and the deltopectoral crest extends distally from the massive greater tubercle beyond the half of the diaphysis. Megalonychidae are represented by a small anterior “spout” of a dentary. Several humerus, tibia and carpal-tarsal bone fragments complete the Tardigrada remains. The study of sloth remains from Quebrada Fiera will allow: 1/ enhancing our knowledge of basal megalonychid and mylodontid sloths, 2/ testing the monophyly of the orophodontoids and their relationship with other mylodontoid sloths, 3/ establishing a possible correlation of central (Bolivia) and southern (Patagonia, Argentina) South American Deseadan sloth faunas. It will also shed light on the basal dispersion of major sloths clades and perhaps also on the origin of Tardigrada.