Brain evolution in fossil rodents: A starting point

Abstract

The goal of this chapter is to summarize work published on virtual endocasts of extant and extinct rodents and provide a framework to answer outstanding questions. Virtual endocasts are known for members of Ischyromyidae, Sciuroidea and Caviomorpha. The study of these rodent endocasts has the potential to help us better understand the condition of the common ancestor of all Euarchontoglires. Early rodents exhibit a simple brain comparable to other early members of Euarchontoglires including fairly large olfactory bulbs, an exposed midbrain and a small neocortex. The study of rodent endocasts provides a snapshot into the potential for deeper understanding that comes from not only estimating endocranial volume but examining comparative quantitative data for different regions of the endocast. A relationship between locomotor behavior and endocranial shape and size appears to exist in rodents, with arboreality as a potential driver for encephalization, and for neocortical and petrosal lobule expansion, in early Sciuroidea; whereas fossoriality may have led to an opposite pattern, with a reduction in the relative size of these two portions of the brain.