What is Diapsid?
[[File:Skull_diapsida_1.svg|thumb|right|230px|alt=Diagram of the diapsid skull|General diagram of the diapsid skull. Note the two holes in the skull behind the eye]] [[File:Allosaurus skull SDNHM.jpg|thumb|230px|''Allosaurus'' skull]] [[File:Massospondylus Skull Steveoc 86.png|thumb|250px|This ''[[Massospondylus]]'' skull shows the two temporal fenestrae typical of diapsids, plus the antorbital fenestra in fron of the eyes.]] A '''diapsid''' is a [[reptile]] with two fenestrae (holes) behind the eye on each side of its [[skull]]. Most reptiles are diapsids, and the condition does not occur in [[mammal]]s. The function of the holes is to improve jaw movements, and to reduce the weight of the skull. The holes give places for muscle attachment; also, as jaw muscles contract, the holes allow space for the muscles to bulge. The ''[[Allosaurus]]'' skull shows the way the skull became lighter in [[dinosaur]]s, especially the large [[theropod]]s. It is here not much more than a series of struts, yet provides massive bite power. == Euryapsids == Some aquatic reptile groups lost the lower of the two openings, leaving just one behind the eye. This is called the '''euryapsid''' condition. It is fairly certain that this is secondary, and that the groups were originally diapsids. The groups include: *[[Ichthyosaur]]s *[[Plesiosaur]]s *[[Placodont]]s [[Image:Skull_euryapsida_1.svg|thumb|left|235px|A euryapsid skull]] [[Category:Reptiles]] [[Category:Skeletal system]]