A new nothrotheriid xenarthran from the early Pliocene of Pomata-Ayte (Bolivia): New insights into the caniniform–molariform transition in sloths

Tardigrade xenarthrans are today represented only by the two tree sloth genera Bradypus and Choloepus, which inhabit the Neotropical rainforests and are characterized by their slowness and suspensory locomotion. Sloths have been recognized in South America since the early Oligocene. This monophyletic group is represented by five clades traditionally recognized as families: Bradypodidae, Megalonychidae, Mylodontidae (†), Megatheriidae (†) and Nothrotheriidae (†). A new nothrotheriid ground sloth represented by a dentary and several postcranial elements, Aymaratherium jeani gen. nov., sp. nov., from the early Pliocene locality of Pomata-Ayte (Bolivia) is reported. This small- to medium-sized species is characterized especially by its dentition and several postcranial features. It exhibits several convergences with the ‘aquatic’ nothrotheriid sloth Thalassocnus and the giant megatheriid ground sloth Megatherium (M.) americanum, and is interpreted as a selective feeder, with good pronation and supination movements. The tricuspid caniniform teeth of Aymaratherium may represent a transitional stage between the caniniform anterior teeth of basal megatherioids and basal nothrotheriids (1/1C-4/3M as in Hapalops or Mionothropus) and the molariform anterior teeth of megatheriids (5/4M, e.g. Megatherium). To highlight the phylogenetic position of this new taxon among nothrotheriid sloths, we performed a cladistic assessment of the available dental and postcranial evidence. Our results, derived from a TNT treatment of a data matrix largely based on a published phylogenetic data set, indicate that Aymaratherium is either sister taxon to Mionothropus or sister to the clade Nothrotheriini within Nothrotheriinae. They further support the monophyly of both the Nothrotheriinae and the Nothrotheriini, as suggested previously by several authors.Fil: Pujos, François Roger Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: De Iuliis, Gerardo. University of Toronto; Canadá. Royal Ontario Museum; CanadáFil: Mamani Quispe, Bernardino. Museo Nacional de Historia Natural; BoliviaFil: Adnet, Sylvain. Université de Montpellier; FranciaFil: Andrade Flores, Ruben. Museo Nacional de Historia Natural; BoliviaFil: Billet, Guillaume. Universite de Paris VI; FranciaFil: Fernández Monescillo, Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marivaux, Laurent. Université de Montpellier; FranciaFil: Münch, Philippe. Université de Montpellier; FranciaFil: Pramparo, Mercedes Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Antoine, Pierre Olivier. Université de Montpellier; Franci