New insights in the evolutionary history and the paleobiology of the ground sloth Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano

BOSCAINI, ALBERTO; GAUDIN, TIMOTHY J.; MAMANI-QUISPE, BERNARDINO; ANTOINE, PIERRE-OLIVIER; PUJOS, FRANÇOIS

Paris

Congreso; 5th International Palaeontological Congress; 2018

Fossil remains of ground sloths have been discovered in numerous localities throughout the Americas, but knowledge of these animals remains poor in the tropical latitudes, in comparison with other extinct folivoran taxa from more northern and southern regions. During the Pliocene, mylodontine ground sloths were spread from North to South America but, in the central regions of South America, well-preserved craniodental remains had not been discovered yet, impeding reliable assessment of their taxonomic attributions and phylogenetic affinities. Recent paleontological expeditions to Pliocene deposits of the Bolivian Altiplano (i.e., localities of Choquecota, Pomata-Ayte, Casira, Inchasi and Ayo Ayo-Viscachani) provided several new well-preserved craniodental remains ascribable to the mylodontid species Simomylodon uccasamamensis. The analysis of this material, and its comparison with other moderate-sized Mio-Pliocene Mylodontinae from North and South America, allowed us to reliably differentiate Simomylodon uccasamamensis among these taxa on both morphological and morphometric grounds, and to revise the taxonomic attributions of several specimens from Bolivia and Argentina. Morphometric analyses show that the species Simomylodon uccasamamensis, together with the poorly-known Glossotheriopsis pascuali, is the smallest Mio-Pliocene mylodontine, whereas new phylogenetic analyses stress the close relationship between Simomylodon uccasamamensis and the late Miocene mylodontine Pleurolestodon acutidens from Argentina. Preliminary studies on the enlarged sample of this Andean mylodontid species suggest the presence of moderate sexual dimorphism, recognizable in both shape and size. These observations are in accordance with those made for some Pleistocene ground sloths (e.g., Paramylodon and Eremotherium), suggesting that sexually dimorphic taxa were already present in the Pliocene Epoch. Simomylodon uccasamamensis also appears to be an endemic taxon of the Andean highlands during the Pliocene, consistently recovered from this area throughout the Montehermosan, Chapdamalalan, and early Marplatan South American Land Mammal Ages. This ground sloth may have found its ideal ecological con- ditions in the Bolivian Altiplano, during a span of time falling between the South American Mio-Pliocene faunal turnover and the Great American Biotic Interchange.