Paleoneurology of extinct cingulates and insights into their inner ear anatomy

Abstract

Xenarthrans, a largely endemic group originating in South America, constitute one of the four major clades of placental mammals. The order Cingulata is composed of extant and extinct xenarthrans that possess a carapace formed by dermal ossicles, i.e. armadillos, pampatheres and glyptodonts. Towards the end of the nineteenth century the study of natural endocasts showed that the brain of glyptodonts was small relative to their body size, with an unusual external neuroanatomy, particularly due to the large size of the olfactory bulbs and cerebellum, and the lissencephalic neocortex. Recently, CT scans allowed us to increase our knowledge of cingulate paleoneurology, including glyptodonts and pampatheres. These new analyses largely corroborate early observations of the glyptodont brain, and show that the pampathere brain presents differences with both glyptodonts and armadillos. Furthermore, it has allowed to reconstruct their inner ear anatomy. Some functional aspects of cingulate paleobiology has also been inferred from the anatomy of the semicircular canals. These analyses have allowed us to obtain a more complete picture of the paleoneurological evolution in this group of mammals. However, more specimens and new species are still needed to better understand their intraspecific variation, as well as their evolutionary patterns and functional implications.