Late Paleogene xenarthrans from Quebrada Fiera (west-central Argentina): implication for the paleogeography of cingulates (armadillos and glyptodontids) and the basal condition in megatherioid and mylodontid sloths

CIANCIO, MARTÍN R.; FRANÇOIS, PUJOS; CERDEÑO, ESPERANZA

Paris

Congreso; 5th International Paleontological Congress; 2018

Paleontological Society

Late Oligocene vertebrate faunas are uncommon in South America. The Argentinean locality of Quebrada Fiera was first noted by Gorroño and colleagues during the 1980s. Recently, more than a dozen field expeditions have revealed an abundant and diverse mammalian fauna, mainly composed of notoungulates but also with representation of marsupials, rodents, and xenarthrans. A lizard and a giant carnivorous bird complete the vertebrate assemblage. Here we present its highly diversified armored xenarthrans and one of the oldest sloth assemblages of America. Hundreds of isolated scutes reveal the existence of eleven cingulates. Dasypodid armadillos are represented by Stenotatus ornatus and two species of Meteutatus (M. lagenaformis and a new species), and a new genus of Euphractini. Peltephilids are represented by two species of Peltephilus (P. undulatus and a new species). Giant Glyptodontidae are represented by Glyptatelus cf. tatusinus and cf. Clypeotherium, a taxon of uncertain affinities, a Propalehoplophorinae, and the palaeopeltid Palaeopeltis inornatus. Cranial and post cranial remains suggest the presence of three sloths, two species of the mylodontid Octodontotherium (O. cf. grande and a smaller species), and a small sized megatherioid Megalonychidae. Octodontotherium teeth are constituted by a thin peripheral wall of cementum, a thick orthodentine layer, and a reduced central core of vasodentine. Lumbar vertebrae of Octodontotherium preserve the oldest evidence of xenarthry in the order, with supplementary intervertebral joints, reduced anapophyses, and short diapophyses. Its hind limb is markedly curved and the knee joint includes an ossified meniscus and a cyamo-fabella, which contribute to the characteristic locomotion of ?ground sloths.? The second mylodontid referred to Octodontherium is represented by a short, bulky humerus with a massive deltopectoral shelf, a deep entepicondylar foramen, and a gigantic entepicondyle. The small megatherioid possesses a reduced lower caniniform followed by a diastema and a Hapalops -like astragalus but with fused ectal and sustentacular facets. The mammalian assemblage of Quebrada Fiera is now well known with about thirty taxa, principally native ungulates and endemic xenarthrans, and almost all groups of mammals present at that time in SouthAmerica are represented. Its composition, clearly Deseadan in age, reveals a mix of taxa represented only in this locality or reflecting a strong austral influence.