First occurrence of Proterotheriidae (Mammalia, Litopterna) in Jujuy Province (Guanaco Formation, Late Miocene), Argentina

Abstract

Proterotheriidae is a family of litopterns within the South American native ungulates, comprising 28 genera ranging from the late Oligocene to the Early Holocene and typically characterized by browsing diets and cursorial adaptations. Remains of this family are scarce in northwestern Argentina and, until now, were unknown from Jujuy Province. We report a proterotheriid specimen (JUY-P 216), recovered from the Guanaco Formation (Fm.) outcropping in Alto Padilla neighborhood, near Río Chico locality, Jujuy Province. Descriptive and quantitative analyses of the fragmentary cranial remains indicate affinities with the genus Neobrachytherium. JUY-P 216 presents quadrangular upper molars with parastyle and mesostyle more developed than the metastyle as in the species of Neobrachytherium; non-divergent premaxillae and incisors with an elliptical cross-section similar to N. ullumense, the incisor–P1 diastema is similar in length to that of N. intermedium, longer than in N. ullumense, and shorter than Epitherium laternarium. This material represents the northernmost record of proterotheriids in Argentina, the first record of this family in Jujuy Province, the earliest litoptern record for the province, and the first native ungulate of the Guanaco Fm. The stratigraphic position suggests that this proterotheriid lived during the Late Miocene Messinian stage, constituting a new faunistic element of the middle section of the Guanaco Fm., from which rodents and xenarthrans have been described. This record adds to previously proposed late Neogene biogeographical patterns for the genus and other herbivorous mammals, and also contributes to the paleoecological characterization of the Late Miocene communities in the Subandean Ranges.