First record of Posnanskytherium (Notoungulata, Toxodontidae) in the late Neogene of eastern Puna, Argentina.

Records of the toxodontid Posnanskytherium were only known from the Pliocene levels of the Bolivian Altiplano and southern Peru. Posnanskytherium desaguaderoi (type species), P. inchasense, P. viscachanense, and P. pacis are the four species recognized so far. In this contribution, we present the first remains of Posnanskytherium desaguaderoi (incomplete skull and fragmentary mandibles) from the Casira locality (Upper Member of the Tafna Formation, Pliocene), eastern Puna, Jujuy Province, Argentina, and provide an extended diagnosis of the genus and the type species. A new phylogenetic analysis recovers Posnanskytherium as a monophyletic clade, with P. desaguaderoi as the sister taxon of P. inchasense and P. viscachanense. The body mass calculated for all Posnanskytherium species indicates that P. desaguaderoi has an intermediate body mass between the higher values corresponding to P. viscachanense and P. inchasense and the lower value of P. pacis. This finding from the eastern Argentinean Puna constitutes the northernmost record of a toxodontid in Argentina, the first appearance of Posnanskytherium in the country, the southernmost record of the genus, and it reinforces the paleofaunistic similarity with the Bolivian Altiplano. Evidence shows that the genus Posnanskytherium had a wide distribution during the late Neogene, ranging from southern Peru to northern Argentina, reaching a greater diversification in the Bolivian Altiplano during the Pliocene. [ABSTRACT FROM AUTHOR]