Earlier we looked at possible eyeball orientations for a basal tetrapod (amphibian) with orbits on top of its skull. The procolophonid, Hypsognathus (Fig. 1) is similar, only the orbit is so large that the eyeball shares the space with bulging temporal muscles.
Even though the skull is quite odd, the eyeballs probably were oriented laterally, to scan the horizon, not the sky. When the orbit and jaw muscles fill the same space, as they also do in basal mammals, every time the jaw muscle moves it changes ever slightly the eyeball shape, either pushing it or relaxing it. Evidently this was not such a big problem for Hypsognathus or basal mammals, because Nature did not correct it. However, when you get to primates, the plate at the back of the primate orbit prevents this interaction because sharp eyesight is paramount for these tree dwellers with binocular vision.
Procolophonids descend from basal diadectomorphs, plant eaters that had to watch out for predators. They produced no descendants.
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