Plohophorini glyptodonts (Xenarthra, Cingulata) from the late Neogene of northwestern Argentina. Insight into their diversity, evolutionary history, and paleobiogeography

Abstract

Northwestern Argentina (NWA), together with the Pampean region (PR), has produced one of the most complete late Neogene continental sequences in Argentina. A diversity of palaeofauna has been recognized from NWA, among which glyptodonts stand out due to the high abundance of their remains. Recent evidences suggests that the Late Miocene was a period of extra-Patagonian diversification in southern South America for glyptodonts, perhaps stimulated by the expansion of C4 grasses and open environments; this has been called the as “Edad de las Planicies Australes”. Here, we focus on one of NWA's most poorly known clades of glyptodonts, the Plohophorini, from the Villavil-Quillay Basin (Catamarca Province). Our results show that, like other clades (e.g., Doedicurini), a single species can be recognized, Stromaphorus ameghini (Ameghino, 1889; ex Moreno, 1882), whose stratigraphic record spans the latest Miocene to the Pliocene (ca. 7.14–3.3 Ma; Messinian-Zanclean). Cladistic analysis confirms the status of the tribe Plohophorini as a natural group within Hoplophorinae (“austral clade”), in which S. ameghini appears as the sister species of the Pampean species S. trouessarti (Moreno, 1888) comb. nov. The oldest precise records of S. ameghini (ca. 7.14 Ma) provide a minimum age for the Plohophorini lineage. The evidence suggests that the diversity of glyptodonts from the late Neogene of NWA is composed of endemic species that are different from those of the PR; however, both areas share the same genera, as observed in other mammalian clades such as Hegetotheriidae (Notoungulata) and Dasypodidae. The cladistic analysis reveals, in a broader context, that the spine-like structure observed in the caudal tube of some genera (i.e., Nopachtus, Propanochthus, and Panochthus) is a homologous structure rather than a convergence as usually interpreted. By contrast, the similar ornamentation pattern represented by the multiplication of peripheral figures in the carapaces of the genera Stromaphorus and Nopachtus is, in fact, a convergence.