INTERPRETACION DEL MOLDE ENDOCRANEANO DE EUCHOLOEOPS FRONTO, UN MEGALONYCHIDAE (MAMMALIA, XENARTHRA, TARDIGRADA) DEL MIOCENO TEMPRANO DE PATAGONIA (ARGENTINA).

Abstract

The brain of Eucholoeops pronto, an Early Miocene Tardigrada from Patagonia, is studied. This is the first paleoneurologic study of an extinct Megalonychidae, a group today represented only by sloths of genus Choloepus. The neocortical sulci are homologous to those found in living Tardigrada, Bradypus (Megatheriidae) and Choloepus (Megalonychidae). These share a common brain pattern, but differences on the neocortical sulci can be noted. Choloepus pattern is more complex than Bradypus one. E. fronto, although a Megalonychidae, has a brain with a Megatheriidae neocortical pattern. The Megalonychidae Ortotheriinae, structural ancestor of living Choloepodinae, is less gyrencephalic with respect to the last one. These neuromorphological traits would be consistent with the more generalized traits that define the Ortotheriinae. During the Early Miocene the morphological differences that do display between the brains of recent Megatheriidae and Megalonychidac could not be shown. Indices of encephalization computed for E. fronto suggest that its brain stands close to the size expected for a modern Megalonychidae.