The supra-occipital bone in cetaceans and burrowing rodents. Morphologicalconvergence induced by the post-cephalic pole?

A comparative study of the cranial morphologies of cetaceans and of rodents tl-lat use their incisors for burrowing brings out morphological convergen ces concerning the supra-occipital bone. These phyletically very remote gro ups are both subject to the same mechanical constraint, viz. the need for t he spinal column to be aligned with the anteroposterior axis of the skull. This constraint, which is related to swimming in cetaceans and burrowing in rodents, entails three major points of convergence: 1) a clearly backward facing foramen magnum; 2) a shortened or even greatly shortened neck, somet imes with cervical vertebrae fused together; and 3) an uprighted or even fo rward tilted supra occipital bone. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.