Evolutionary disparity in the endoneurocranial configuration between small and gigantic tyrannosauroids

ABSTRACTIn extinct archosaurs, brain proportions have been inferred from the morphology of fossilized endocasts. Here we provide the first neurocranial and paleoneurological description of the basal, small-bodied tyrannosauroid Dilong paradoxus compared with larger tyrannosaurids, like Tyrannosaurus rex. Dilong differs from other tyrannosauroids in the proportions of cerebral and cerebellar regions, morphology of venous sinuses, and superimposed position of the forebrain relative to the rest of the endocast. Whereas endocasts of Tyrannosaurus show a more linear configuration and likely contained within a thick intersticial space, the endocast of Dilong indicates an S-shaped brain protected by thinner meninges. Based on our statistic analysis and comparisons with modern crocodilians, we hypothesize that increased body size likely imposed a new spatial configuration for development of the central nervous system during the evolution of gigantism in tyrannosaurs.