Allosaurus, crocodiles, and birds: Evolutionary clues from spiral computedtomography of an endocast

Because the brain does not usually leave direct evidence of its existence i n the fossil record, our view of this structure in extinct species has reli ed upon inferences drawn from comparisons between parts of the skeleton tha t do fossilize or with modern-day relatives that survived extinction. Howev er, soft-tissue structure preservation may indeed occasionally occur, parti cularly in the endocranial space. By applying modern imaging and analysis m ethods to such natural cranial "endocasts," we can now learn more than ever thought possible about the brains of extinct species. I will discuss one s uch example in which spiral computed tomography (CT) scanning analysis has been successfully applied to reveal preserved internal structures of a natu rally occurring endocranial cast of Allosaurus fragilis, the dominant carni vorous dinosaur of the late Jurassic period. The ability to directly examin e the neuroanatomy of an extinct dinosaur, whose modern-day relatives are b irds and crocodiles, has exciting implications about Allosaurus' behavior, its adaptive responses to its environment, and its eventual extinction. Ana t Rec (New Anat) 257:162-173, 1999. (C) 1999 Wiley-Liss, Inc.