Digital cranial endocast of Pseudoplohophorus absolutus (Xenarthra, Cingulata) and its systematic and evolutionary implications

ABSTRACT

Glyptodonts are a group of extinct xenarthrans with several anatomical features that make them one of the most bizarre groups of mammals. By the late 19th century, some authors began to analyze the brain of Pleistocene glyptodonts using natural endocranial casts. These studies revealed the small size of the brain of the large Pleistocene forms. However, the evolution of the brain in glyptodonts and how it fits in a phylogenetic context has not been analyzed. In order to evaluate the evolution of the brain in this group, we described the first digital endocranial cast of the late Miocene glyptodont Pseudoplohophorus absolutus and compared it with digital endocranial casts of the Pleistocene glyptodonts Glyptodon, Doedicurus, and Panochthus and the extant armadillos Dasypus, Euphractus, Chaetophractus, and Zaedyus. The endocast morphology of P. absolutus is similar to that of Pleistocene glyptodonts: large olfactory bulbs, a small cerebrum with a single neocortical sulcus, and a large cerebellum. However, the relative brain size is larger than in the Pleistocene forms, with values of the encephalization quotient (EQ) close to that of extant armadillos. A comparison between xenarthrans orders shows that Cingulata (glyptodonts and armadillos) have lower EQ values than Pilosa (sloths and vermilinguas). This could possibly be related to certain restrictions and benefits imposed by the presence of the carapace in cingulates. Furthermore, because the carapace restricts the development of the cervical musculature that supports the skull, the small size of the brain in glyptodonts could be a trade-off (along with others) to reduce the weight of the skull.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ACKNOWLEDGMENTS

We are grateful to M. E. Castelló and S. F. Vizcaíno for valuable suggestions. Thanks to reviewers G. Billet and K. Porpino and the editor M. Sánchez-Villagra for comments and corrections that improved the manuscript. Thanks to S. Olivieri and the technical staff of Hospital Mautone for their assistance in the CT scans of the skulls. Thanks to S. Patiño for improving the English text. ANII (Agencia Nacional de Investigación e Innovación) grant BE_POS_2010_1_2195 to PST partially supported this research.