Skull Ichthyosaur

the skull of temnodontosaurus platyodon has typical ichthyosaurian shape elongated snout , large eye sockets.

basal ichthyopterygia had elongated triangular skull. ichthyosaurs in narrow sense, snout became pointy. snout formed premaxilla. maxilla behind shorter , excluded external nostril rear branch of premaxilla. accordingly, number of premaxillary teeth high, while maxillary teeth fewer in number or absent. rear top of snout formed nasal bones. derived species have foramen internasale, midline opening separating rear of nasal bones. nasal bone forms top , front rim of bony nostril, placed in front of eye socket. however, triassic species, premaxilla extended @ excludes nasal nostril.

the rear of skull dominated large eye socket, covering major part of rear side surface. in socket, large scleral ring present; circular structure of small, overlapping bone segments protecting eye against water pressure. both in relative , absolute senses, ichthyosaurs have largest eye sockets of known vertebrates. other rear skull elements typically compressed , fused difficult identify. top rear element of skull assumed supratemporal bone, while squamosal , quadratojugal fused. however, in 1968, alfred sherwood romer stated presumed supratemporal in fact squamosal, in 1973 confirmed mcgowan. in 1990, though, john steve massare convinced researchers original identification had been correct 1 after all. supratemporal forms rear rim of supratemporal opening; lower temporal opening @ side lacking. front rim of supratemporal opening typically formed postfrontal; basal utatsusaurus postorbital , squamosal still reach edge. between paired supratemporal openings, skull roof narrow; species have longitudinal crest on attachment jaw muscles. basal ichthyopterygia have parietal eye opening between paired parietal bones. ichthyosaurs proper, opening moves front, first border between parietals , frontals , between frontals, condition shown derived species. postparietal , tabular bones lacking. often, bones of of skull , palate incompletely ossified, apparently having partly remained cartilage. occipital condyle typically convex. stapes, bone transmitting sound waves eardrum middle ear, elongated , not pierced foramen. pterygoid teeth typically lacking.