Evolution of Neosclerocalyptus Paula Couto (Cingulata, Glyptodontidae, Hoplophorini) during the early Pleistocene-early Holocene: associated palaeoenvironmental changes

ZURITA A.E.; SCARANO A.C.; CARLINI A.A.; SCILLATO-YANÉ G.J.; SOIBELZON E.

Río de Janeiro

Simposio; 7º Simposio Brasileiro de Paleontologia de Vertebrados; 2010

SBPV

One of the Glyptodontidae (Mammalia. Xenarthra) most frequently recorded in southern South America (17° 47` S and 63° 11´W. and 38° 10´ S and 58° 48´ W) is Neosclerocalyptus Paula Couto, whose main apomorphy is a notable and progressive development of the fronto-nasal sinuses, a feature unique among glyptodonts. Here we present new evidence of the correlation between palaeoclimatic-environmental processes occurred during the early Pleistocene- early Holocene and the evolution of fronto-nasal sinuses. Four species are recognized during the last million years (N. pseudornatus, ca. 1.07-0.98 Ma; N. omatus, ca. 0.98-0.78 Ma; N. gouldi, ca. 0.40-0.13 Ma; and N. paskoensis. ca. 0.13-0.011 Ma), and each of them seems to have replaced the previous one, most likely via anagenesis. The lirst record (N. pseudomatus) coincides with the ?Great Patagonian Glaciation" (OIS 30-34), and is characterized by an incipient degree of development and pneumatization of the fronto-nasal sinuses. Thus, an interesting correlation is observed between the appearance of this character and a cooling period represented by one of the largest glaciations of the Pleistocene. Later on, the distribution of species of this genus is associated with  loessic (cold arid and semiaridi environments, where they are, together with Glyptodon Owen, the most abundant record of Glyptodontidae; in contrast, their records are very scarce or absent in areas that had warmer and more humid environments (e.g. Argentine Mesopotamia, western Uruguay and south em Brazil). We propose that the particular low latitudinal distribution of this taxon and the cyclic nature of the glacial-interglacial events during the mostly arid and cold Pleistocene were factors that probably stimulated rapid morphological evolution of the fronto-nasal sinuses in this clade. ln this context, the specimens of N. paskoensis (the most derived species), limited to OIS 2 (ca. 28-10 ka), show the greatest development and pneumatization of these particular anatomical structures, with clearly trabecular intemal morphology. its geographical distribution learly coincides with the distribution of loess, deposited mostly under the cold arid conditions characteristic of OIS 2. This situation suggests strong correlation between climatic variables and morphological changes. Finally, evidences such as the limited latitudinal distribution of the genus and the replacement of one species by another suggest the existence of a single successive lineage of species.