Evolution of Gyrification in Carnivores.

The order Carnivora is a large and highly diverse mammalian group with a long and well-documented evolutionary history. Nevertheless, our knowledge on the degree of cortical folding (or degree of gyrification) is limited to just a few species. Here we investigate the degree of cortical folding in 64 contemporary and 37 fossil carnivore species. We do so by measuring the length of gyri impressions on endocranial casts. We use this approach because we have found that there is a very good correlation between the degree of cortical folding and the relative length of the gyri that are exposed on the outer surface of the hemispheres. Our results indicate that aquatic and semiaquatic carnivores have higher degrees of cortical folding than terrestrial carnivores. The degree of cortical folding varies among modern families, with viverrids having the lowest values. Furthermore, the scaling of cortical folding with brain size follows different patterns across specific carnivore families. Forty million years ago, the first carnivores had a relatively small cortex and limited cortical folding. Both the size of the cortex and the degree of cortical folding increased independently in each family during evolution.