Neuroanatomy of the giant caviomorph Eumegamys paranensis (Dinomydae, late Miocene, Argentina)

CANDELA, A.M.; TAMBUSSI, C.P.; DEGRANGE, F.J.

General Roca

Congreso; 11 Congreso de la Asociación Paleontológica Argentina; 2016

Asociación Paleontológica Argentina

Eumegamys paranensis Kraglievich (1926) is an extinct dynomid rodent registered during the late Miocene in the eastern mesopotamic area of Argentina. By modern standards, it was a giant rodent with a body mass estimation of more than 100 kilos. During the late Miocene the family exhibits its greater taxonomic richness, morphological disparity and ecological diversity including the development of various giant taxa. 3D virtual models constructed from CT scans of the skull MLP 41-XII-13-237, allow us to describe details of brain anatomy for the first time. The cerebrum is lissencephalic, with large olfactory bulbs cranially disposed and not covered by the frontal lobes, an elongated circular fissure, a deep sylvian sulcus, marked rhinal fissure, a large pituitary gland; and cerebellum with vermis and paramedian fissures absent, lateral lobes poorly extended caudally and absent paraflocculus. The most striking feature is the great expansion of the transverse and sigmoid sinuses, covering the colliculi, and the great development of nerve V. Both sinuses are interconnected and drain into the internal jugular vein. On its part, the action of the colliculi is related, but not exclusively, with eye and head movements. So far, the brain features have not been applied in studies of relationship among Caviomorpha and could be useful in providing data regarding the closest affinities of the Dinomyidae. This study provides an interesting perspective to understand the evolution of the rodent brain and particularly the evolution of gigantism within Rodentia