Skull Shape and Size Diversification in the Genus Ctenomys (Rodentia: Ctenomyidae)

The genus Ctenomys is comprised of more than 70 valid living species. It is the largest collection of fossorial mammals that occupy underground habitats, mainly in the grasslands of South America. We investigated different aspects of morphological evolution in the genus Ctenomys, with special attention to the skull. We analyzed 1359 craniums and 830 mandibles of 49 species of Ctenomys. We used geometric morphometric approaches to quantify this morphological diversity across its range. We found geographical structuring in skull shape among the eight clades of Ctenomys structured along east-west and north-south morphological gradients. We observed that many species from the extreme north of the distribution had a robust skull shape, whereas the southern ones had a gracile skull shape. Such structural differences may be following an environmental gradient. The mandible is less variable in shape than the cranium. We found high morphological variation within each of the eight clades and a geographical structuring. The subterranean niche is not homogeneous across space, and morphological adaptation of subterranean species occurs following this spatial gradient.