A new species of Plohophorus Ameghino (Cingulata, Glyptodontidae) from the latest Pliocene–earliest Pleistocene of the Pampean Region (Argentina): the last survivor of a Neogene lineage

AbstractWithin xenarthrans, two large groups are recognized, Pilosa (anteaters and sloths) and Cingulata (armoured xenarthrans). The latter contains Glyptodontidae, one of the most bizarre and enigmatic groups of animals that ever lived. Recent phylogenetic proposals show an early Miocene divergence into two clades, one of northern origin (Glyptodontinae) and the other with its oldest records in the early–middle Miocene of southern South America, which groups most of the recognized diversity. Although knowledge of the ‘austral clade’ has increased recently, several taxa need urgent taxonomic and phylogenetic studies to understand their evolutionary history. One case is represented by the ‘Plohophorini’, a tribe that traditionally included several genera (Plohophorus, Pseudoplohophorus, Phlyctaenopyga, Stromaphorus and Stromaphoropsis), from the late Miocene–Pliocene of the Pampean and North-Western regions of Argentina, and Uruguay. A new and terminal species of Plohophorus, P. avellaneda sp. nov., coming from the El Polvorín Formation (Pampean region of Argentina) is here reported and described, and represents the first case of a Neogene genus of glyptodont crossing the Plio–Pleistocene boundary (c. 2.53 Ma). In addition, the palaeohistological analysis on the osteoderms (the first for ‘Plohophorini’) reveals some characters not observed in other glyptodonts, highlighting its potential phylogenetic importance. The phylogenetic analysis corroborates that the well-characterized species of ‘Plohophorini’ of Uruguay and the Pampean region of Argentina (‘eastern Plohophorini’) constitute a natural group within the austral clade, since both species of Plohophorus (P. avellaneda + P. figuratus) cluster together, and are the sister taxa of Ps. absolutus + Ps. benvenutti. Along the evolutionary history of Plohophorini an increase in body mass is observed, reaching its maximum with P. avellaneda sp. nov. (c. 471 ka). Despite the high frequency of late Pliocene records, Plohophorini disappear completely from the fossil record during the Pleistocene, suggesting that this character was negatively selected.http://zoobank.org/urn:lsid:zoobank.org:pub:FF11606C-2F27-4309-9DFD-FA74E769E639Keywords: glyptodontsevolutionary history‘austral clade’morphologypalaeohistology AcknowledgementsThe authors of this contribution would like to express their gratitude to the heads of the institutions for allowing us access to the collections and the study of the material under their care. We also thank the company ‘Cementos Avellaneda S. A.’ for promoting and supporting research in palaeontology and for allowing us to study the material. We also thank both the anonymous reviewers and the associate editor, whose comments and suggestions greatly improved the manuscript. This contribution was partly funded by the projects PI Q002/17 (SGCyT-UNNE) and PICT 0765/17 (FONCyT).Supplemental materialSupplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2023.2246963.Associate Editor: Alistair Evans