Neosclerocalyptus Paula Couto (Xenarthra, Glyptodontidae) in the late Pliocene-earliest Pleistocene of the Pampean region (Argentina): Its contribution to the understanding of evolutionary history of Pleistocene glyptodonts

Abstract

Glyptodontidae are a conspicuous lineage of Cingulata with a long evolutionary history (late Eocene to the late Pleistocene-Holocene). Quaternary forms are the best known, but in recent years the knowledge of Neogene taxa, particularly from southern South America has been greatly improved. This is especially evident for the late Miocene-Pliocene (Montehermosan and Chapadmalalan Stages; ca. 5–3.2 Ma) of the Argentine Atlantic coast. However, little is still known about the glyptodont assemblages from the Marplatan Stage (ca. 3.3–2 Ma), a key interval for the understanding of the typical Pleistocene forms. The most complete records of Marplatan Glyptodontidae of the genus Neosclerocalyptus Paula Couto (one of the most frequently recorded in the Pleistocene of southern South America) are here reported. The remains were found in the El Polvorín Formation (Olavarría, Buenos Aires Province) and represent also the most complete glyptodonts for the interval Montehermosan-Marplatan of the Argentine Atlantic coast. The comparative study reveals that Neosclerocalyptus underwent no significant morphological and morphometric changes throughout its evolution (ca. 3 Ma), except for a gradual increase in hypertrophy of the ossified nasal cartilages, which reach the maximum development in the terminal species of the latest Pleistocene, Neosclerocalyptus paskoensis. The phylogenetic analysis places Neosclerocalyptus sp. as the most basal taxon of the lineage, suggesting the anagenetic evolution of the clade. New findings currently under study show that some taxa (e.g., Plohophorus) extended their biochrons beyond the Chapadmalalan, with a strong increase of body size, and that the Marplatan was a transitional period between the Montehermonsan-Chapadmalalan and the Pleistocene, during which Neogene genera are found together with others typically Pleistocene.