The last survivor of a Neogene lineage of Glyptodontidae (Xenarthra, Mammalia) : Plohophorusameghino in the latest Pliocene-earliest Pleistocene of the pampean region (Argentina)

Abstract

Xenarthra are divided into two groups, Pilosa (anteaters and sloth) and Cingulata (armored xenarthrans). In this latter, Glyptodontidae constitutes one of the most enigmatic animals that ever lived in South America until its extinction in the latest Pleistocene-Early Holocene. Recent phylogenetic proposals show an early Miocene divergence into two clades, one of northern origin (Glyptodontinae) and the other with austral origin, which groups the majority of the recognized diversity. Despite the fact that the knowledge of the austral clade was recently improved, several taxa need urgent taxonomic and phylogenetic studies in order to understand their evolutionary history. One particular case is represented by the "Plohophorini", a tribe that traditionally included several genera (Plohophorus, Pseudoplophophorus, Phlyctaenopyga, Stromaphorusand Stromaphoropsis), from the late Miocene-Pliocene of Pampean and Northwestern regions of Argentina and Uruguay. In this contribution we present a new and terminal species of Plohophorus (Xen-44, CCA-19 y CCA-20 "Colección Cementos Avellaneda". Olavarría, Buenos Aires) exhumed from the El Polvorín Formation, of the Pampean region of Argentina, which in turn represents the first case of a Neogene genus of glyptodonts surviving into the Plio-Pleistocene limit (ca. 2.53 Ma). Plohophorus sp. nov. differ from P. figuratus by the well-developed lacrimal tubercle; short, stright and wide descending process; occipital condyles with greater transverse development; a third series of peripheral figures between the second and the third series of proximal osteoderms of the caudal tube. The preliminary phylogenetic analysis shows that Plohophorus sp. nov.+ P. figuratus cluster together, being the sister taxa of Ps. absolutus + Ps. benvenutti, corroborating that the well characterized species of Plohophorini of Uruguay and the Pampean region of Argentina constitute a natural group. In turn, the comparative anatomical study shows that Pseudoplophophorus spp. and Plohophorus spp. share several potential synapomorphies with Phl. ameghini and St. compressidens, (late Miocene-Pliocene of Northwestern Argentina). If this hypothesis is confirmed, the tribe Plohophorini, could be interpreted as a natural group containing two radiations, one with eastern distribution (Argentina and Uruguay) and the other restricted to the western region (Argentina).