New Insights Into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior
Article first published online: 26 AUG 2009
Copyright © 2009 Wiley-Liss, Inc.
The Anatomical Record
Special Issue: Unearthing the Anatomy of Dinosaurs: New Insights Into Their Functional Morphology and Paleobiology
Volume 292, Issue 9, pages 1266–1296, September 2009
How to Cite
Witmer, L. M. and Ridgely, R. C. (2009), New Insights Into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior. Anat Rec, 292: 1266–1296. doi: 10.1002/ar.20983
- Issue published online: 26 AUG 2009
- Article first published online: 26 AUG 2009
- Manuscript Received: 9 JUN 2009
- Manuscript Accepted: 9 JUN 2009
- National Science Foundation. Grant Numbers: IBN-9601174, IBN-0343744, IOB-0517257
- Ohio University College of Osteopathic Medicine
- inner ear
The braincase region of tyrannosaurs was investigated to provide insights on anatomical attributes relevant to inferences of sensory biology and behavior. CT scanning focused on three specimens of Tyrannosaurus rex, a juvenile Gorgosaurus, and the controversial Cleveland skull (CMNH 7541). Analysis shows that the cerebral hemispheres were enlarged, but conflicting information on the optic lobes suggests that brain conformation was not fully avian. Previous estimates of olfactory bulb size for T. rex were much too large, but even the corrected sizes are relatively larger than other theropods, suggesting that odor detection was indeed of particular importance to tyrannosaurs. The inner ears show a number of coelurosaurian traits, such as elongate and rounded and rostral, lateral semicircular canals, and incipient twisting of the common crus, which we interpret to be related to enhanced reflexes coordinating rapid eye and head movements. The cochlea is elongate, which, coupled with the finding of extensive tympanic pneumaticity, supports the inference of behavioral emphasis of low-frequency sounds. Three main groups of sinuses pneumatized the braincase, and there are a number of perhaps systematically relevant differences. Orientation of the endosseous labyrinth reveals that alert head postures of T. rex and Gorgosaurus were somewhat depressed below the horizontal, but the Cleveland skull had a very strongly down-turned posture. It is concluded that tyrannosaur sensory biology is consistent with their predatory coelurosaurian heritage, with emphasis on relatively quick, coordinated eye and head movements, and probably sensitive low-frequency hearing; tyrannosaurs apomorphically enhanced their olfactory apparatus. The taxonomic status of the Cleveland skull remains unresolved. Anat Rec, 292:1266–1296, 2009. © 2009 Wiley-Liss, Inc.