The brain of Pampatherium Ameghino; external morphology and comparison with allied genera

Abstract

Palaeoneurological analysis is a useful tool for evolutionary inferences in diverse vertebrate groups, but such studies are scarce regarding the South American Quaternary megamammal fauna. Particularly in xenarthrans, studies have been carried out mainly in the Suborder Pilosa, which includes anteaters, tree sloths and ground sloths. Within Suborder Cingulata, i.e., armadillos, glyptodonts and relatives, an analysis of a digital endocast in a specimen belonging to the genus Glyptodon Owen has recently been performed. We present here the construction and analysis of a digital endocast of another cingulate, namely Pampatherium Ameghino. The cast was made after CT scans, by using the reconstruction software BioVis 3D. This software was also used to display and calculate the volume of the digital cast and the appropriate portions under scrutiny. The external brain morphology of the specimen of Pampatherium shows that the telencephalic hemispheres were poorly sulcated, and does not extend over either the cerebellum or the olfactory bulbs. Compared with digital endocast of three extant armadillos and of Glyptodon, the broad morphology shows a closely resemblance with the latter. These results are consistent with the most recent phylogenetic reconstructions in Cingulata. On the other hand, the body mass estimate from cranial and dental measurements for that specimen of Pampatherium yielded a value of 380kg. From this, a quantitative analysis was performed and the appropriate encephalisation quotient was obtained, which turned out to be 0.25, which is greater than that calculated for the Glyptodon specimen (0.16), whose body mass had been estimated as 1300kg. Both are less than those observed in the three extant armadillos, whose values range from 0.41 to 0.68.