[N] 2005 The oviraptorosaur braincase
Osmólska, H. (2005) Some aspects of the oviraptorosaur (Dinosauria, Theropoda) braincase. 1st Meeting of the EAVP Natural History Museum Basel
Examinations of dinosaur endocasts do not usually give information how close walls of the endocranial cavity lay to the brain surface. It has been assumed by Jerison (1973) that cranial cavity in the fossil reptiles may have had a capacity about twice that of the brain size, which it contained in life. This opinion has not been concurred by Hopson (1979), who considered that this relationship might be
variable in fossil forms as it is in the living reptiles. In birds and mammals, the brain surface is closelyappressed to bones of cranial roof, and it leaves distinct impressions of the intracranial vascular channels on the undersurface of the bones in this region. In dinosaurs, the impressions of the brain vascular system, evidencing a direct contact between the brain surface and the skull roof bones, have been so far reported only in one theropod dinosaur, the ornithomimid, Dromiceiomimus (Russell 1972) and their presence has been suggested (Hopson 1979) in the troodontid, Stenonychosaurus .
Both theropods represent the clade Maniraptoriformes within Coelurosauria. Up to now, it has not been known to which extent the brain filled the braincase in another member of the same clade, the oviraptorids. The here reported case of an oviraptorid representative, Ingenia, shows that in these maniraptorans the brain surface was also appressed to the undersurface of the skull roof, where it left distinct imprints of brain vascularization.
In Ingenia , the imprints of the brain vessels are found on the undersurface of the frontals and parietals. They consist of numerous arborizing grooves, which cover undersurface of the skull roof bones in the region of cerebral hemispheres and the cerebellum. The density and regularity of the vascularization of the brain surface in Ingenia are incomparable to the scarce and irregular ones, previously stated in Dromiceiomimus .
The avialan status of Oviraptoridae has been postulated by some theropod students (e.g. Elżanowski 1999; Lu 2000; Maryańska, Osmólska & Wolsan 2002). The present finding may provide additional evidence supporting this hypothesis.