Anapsid

An anapsid is an amniote whose skull does not have openings on the sides behind the eyes.Pough F.H. et al. 2002. Vertebrate life, 6th ed. Prentice Hall, NJ.  This is
A primitive ('basal') condition for early amniotes in the Mississippian (early Carboniferous).
A secondary ('derived') condition of some other reptile groups, probably including turtles (Chelonia).

Some other groups were anapsids, such as the mesosaurs.

 References 

Category:Tetrapods