New material of the extinct sloth Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano: systematic and pelobiological implications

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

Albuquerque

Congreso; 78th Annual Meeting of the Society of Vertebrate Paleontology; 2018

Fossil remains of extinct sloths have been discovered in numerous localities throughout the Americas, but knowledge of these animals remains poor in the tropical latitudes in comparison with sloth taxa from more northern and southern regions. Mylodontine ground sloths were widespread during the Pliocene but, in the central regions of South America, well-preserved craniodental remains were extremely rare, impeding reliable assessment of their taxonomy 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) have provided new well-preserved craniodental remains ascribable to the mylodontid species Simomylodon uccasamamensis. Detailed comparison of this material with other moderate-sized Mio-Pliocene mylodontines from North and South America allowed us to reliably differentiate Simomylodon uccasamamensis from 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 sloths (e.g., Paramylodon and Eremotherium), suggesting that sexually dimorphic sloth 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 sloth may have been specifically adapted to the ecological conditions prevailing in the Bolivian Altiplano at this time, a span falling between the South American Mio-Pliocene faunal turnover and the Great American Biotic Interchange.