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

CERDEÑO, E; PUJOS, F.; CIANCIO, M.R.

París

Congreso; 5th International Palaeontological Congress; 2018

International Palaeontological Association

Late Oligocene vertebrate faunas are uncommon in South America. The Argentineanlocality of Quebrada Fiera was rst noted by Gorro~no and colleagues during the 1980s.Recently, more than a dozen eld 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 diversied armored xenarthrans and one of the oldest sloth assemblages of America.Hundreds of isolated scutes reveal the existence of eleven cingulates. Dasypodid armadillosare represented by Stenotatus ornatus and two species of Meteutatus (M. lagenaformis anda new species), and a new genus of Euphractini. Peltephilids are represented by two speciesof Peltephilus (P. undulatus and a new species). Giant Glyptodontidae are represented byGlyptatelus cf. tatusinus and cf. Clypeotherium, a taxon of uncertain anities, 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 ossied 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 witha massive deltopectoral shelf, a deep entepicondylar foramen, and a gigantic entepicondyle.The small megatherioid possesses a reduced lower caniniform followed by a diastema and aHapalops-like astragalus but with fused ectal and sustentacular facets.