We addressed two aspects of cetacean evolution: their acquisition of a relatively big brain and the evolution of their sense of smell. As other mammals secondarily adapted to the aquatic environment, cetaceans have been assumed to reduce their sense of smell (which is air-born in this group).

Comparing the relative volume of the brain endocast, we found that this early whale was quite brainy, which is a surprise, as the first cetaceans with big brains were so far understood to be the fully aquatic basilosaurids.

We ct-scanned the skull of Protocetus atavus, an amphibious cetacean coming from the Mokattam Formation in Egypt. The inner anatomy of the skull was reconstructed, and we were able to reconstruct the brain imprint (endocast) as well as the different components of the nasal cavity.