in posterior view, with (left) and without (right) the proatlases in place
A number of different interpretations have been made of the proatlas.[2][3] The most common interpretation is that it is the vestigial neural arch of a vertebra that is otherwise fully incorporated into their skull, but the development shows some differences from other vertebrae that present difficulties for this hypothesis.[1]
The proatlas was probably widely present across early tetrapods, and is retained in some modern reptiles, such as the
crocodylians, the left and right proatlases fuse into a single V-shaped midline element.[1][3]
Othniel Marsh, who initially termed them the "post-occipital bones",[6] but their homology with the proatlas of other reptiles was subsequently recognized by Charles W. Gilmore.[7]
