[The mechanism of digging in Arvicola terrestris and Spalax ehrenbergi: functional and evolutional studies]

The cineradiographic study of the digging modalities in Arvicola terrestris and Spalax erenbergi showed important convergences in the mechanisms used by both species. Head and incisors are the burrowing tools, acting as a "scraping-shovel" in Spalax and as a "scratching-shovel" in Arvicola. They are moved forward by a force originated by the pressure of the hind limbs against the ground, and transmitted through the vertebral axis. The myological study of these species revealed the increase of the insertional areas for the cephalic muscles. However, the adaptative answer of the cervical vertebrae to the mechanical constraints of digging are different in Arvicola and Spalax; the former developed high resistance moments and the latter increased vertebral stiffness. The characters of the post-cranial skeleton in the digging rodents tend to constitute a morphocline in which Spalax is the final stage and Arvicola an intermediate stage. Then, the adaptative divergences noted above between these animals might reflect their phyletic distance.