Systematic and morpho-geometric analyses of Pachyrukhinae (Mammalia, Hegetotheriidae) from the Huayquerías, Mendoza (Argentina): Biostratigraphic and evolutionary implications

Abstract

We give to know new remains of Pachyrukhinae (Hegetotheriidae) from the Huayquerías de San Carlos (Mendoza, Argentina). We identify Tremacyllus impressus, proposing T. subdiminutus a synonym name, and giving to know new data of postcranial bones for this taxon. Tremacyllus specimens from Mendoza reveal a wide and continuous morphological variation that encompasses the morphological differences of previously considered valid species, emphasizing the need of a systematic study focused in the whole representatives of the genus. We also recognize Paedotherium typicum which shows a particular combination of features differing from other species of the genus. The large sample allows us to highly improve the diagnosis for both the genus Tremacyllus and the species T. impressus, and P. typicum. Both species coexist in the Huayquerías Formation; T. impressus is also present in the Tunuyán Formation, whereas the specimens recognized as Paedotherium in this unit did not allow us to identify at level species. Applying geometric morphometric methods on dentition, we partially support the systematics decisions. We present the first phylogenetic analysis including all the species of Tremacyllus and Paedotherium, using morphologic characters of skull and postcranium. According to our results, Tremacyllus is a monophyletic group supported by two synapomorphies, while Paedotherium is paraphyletic, agreeing previous hypothesis. The record of Paedotherium typicum here presented extends the biochron of this taxon and increases the diversity of the genus on to the late Miocene, which is relevant to establish biostratigraphic and paleobiogeographic affinities with other Miocene localities