proatlas

A small, paired bony element (more rarely, having fused parts) located between the skull and the atlas in tuataras, crocodiles, chameleons, and many fossil reptiles; it is uncommon in turtles and mammals (hedgehog). The proatlas apparently develops from the ossified neural part of the sclerotome. Externally it resembles the neural arch of the vertebra, since it articulates anteriorly with the lateral occipital bone and posteriorly with the anterior articular process of the atlas.