CONICET | Buscador de Institutos y Recursos Humanos

A new genus and species of Nothrotheriidae (Xenarthra, Pilosa) from the Bolivian Quebrada Honda locality (Laventan South American Land Mammal Age; middle Miocene) is described based on a nearly complete mandible. Nearly a dozen nothrotheriids have been named in the literature, but many are poorly defined and of doubtful validity. The new species is clearly differentiated from the well-diagnosed nothrotheriids, such as Huilabradys, Mionothropus, Nothrotheriops, Nothrotherium, Nothropus, Pronothrotherium, and Thalassocnus. A small caniniform, the plesiomorphic condition, is present, in contrast to Nothrotherium, Nothrotheriops, and Thalassocnus; and is followed by a diastema and three rectangular or quadrangular molariforms with mesial and distal transverse lophids separated by a valley, as is typical of nothrotheriids. The new species differs from other known nothrotheriids in possessing an elongated, wide and spatulate symphyseal spout. The caniniform is displaced laterally to the long axis of the molariform series, presumably in association with the widened spout. As well, the last molariform bears an apicobasal sulcus on its distal surface, which is considered autapomorphic. An internal anterior opening of the mandibular canal is present on the medial surface of the dentary on either side of the symphysis, a condition recorded only in Xyophorus among sloths. The new sloth is the fourth sloth reported from Quebrada Honda, the previously described being Xyophorus villarroeli, Hiskatherium saintandrei, and a Mylodontidae. Quebrada Honda is an important locality for reconstructing the paleomammalian fauna of the South American Miocene and correlating the austral Patagonian faunas to tropical vertebrate faunas (e.g., La Venta in Colombia).