Phylogeny and paleobiogeography of Hegetotheriidae (Mammalia, Notoungulata)

Abstract

Hegetotheriidae are one of the most derived families of the Order Notoungulata. It is composed of two subfamilies: Hegetotheriinae, which resolves as paraphyletic in most recent phylogenies, and Pachyrukhinae, which historically is considered monophyletic. The family is recognized from late Oligocene to Pliocene and is well diversified from its earliest records. Most papers on the family are systematic studies and, to a lesser degree, investigate its phylogenetic relationships, but paleobiogeographic approaches are rare. A phylogenetic analysis was carried out using TNT, based on a previous matrix that was augmented with additional taxa and characters. Previous results are supported, viz., the paraphyly of Hegetotherium Ameghino and Paedotherium Burmeister, and the monophyly of Pachyrukhinae, but new conclusions arise, such as the paraphyly of Hemihegetotherium Rovereto and the monophyly of Prohegetotherium Ameghino and Hegetotheriinae. In this work, a paleobiogeographic analysis on hegetotheriids is carried out by means of the Bayesian method using the RASP program, with the aim of estimating the possible ancestral area and vicariance, dispersal, and extinction events. This analysis shows that Hegetotheriidae and both subfamilies originated in central Patagonia (southeast of Chubut and northeast of Santa Cruz provinces). The analysis also reveals that dispersals were the predominant events, and they are related to Cenozoic dispersals to lower latitudes as global cooling advanced and new lands emerged.