Ben Creisler
A new paper:
Matthew McKeown, Stephen L. Brusatte, Thomas E. Williamson, Julia A. Schwab, Thomas D. Carr, Ian B. Butler, Amy Muir, Katlin Schroeder, Michelle A. Espy, James F. Hunter, Adrian S. Losko, Ronald O. Nelson, D. Cort Gautier & Sven C. Vogel (2020)
Neurosensory and Sinus Evolution as Tyrannosauroid Dinosaurs Developed Giant Size: Insight from the Endocranial Anatomy of Bistahieversor sealeyi.
The Anatomical Record (advance online publication)
doi:
https://doi.org/10.1002/ar.24374https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24374
Tyrannosaurus rex and other tyrannosaurid dinosaurs were apex predators during the latest Cretaceous, which combined giant size and advanced neurosensory systems. Computed tomography (CT) data have shown that tyrannosaurids had a trademark system of a large brain, large olfactory bulbs, elongate cochlear ducts, and expansive endocranial sinuses surrounding the brain and sense organs. Older, smaller tyrannosauroid relatives of tyrannosaurids developed some, but not all, of these features, raising the hypothesis that tyrannosauridâstyle brains evolved before the enlarged tyrannosauridâstyle sinuses, which might have developed only with large body size. This has been difficult to test, however, because little is known about the brains and sinuses of the first largeâbodied tyrannosauroids, which evolved prior to Tyrannosauridae. We here present the first CT data for one of these species, Bistahieversor sealeyi from New Mexico. Bistahieversor had a nearly identical brain and sinus system as tyrannosaurids like Tyrannosaurus, including a large brain, large olfactory bulbs, reduced cerebral hemispheres, and optic lobes, a small tabâlike flocculus, long and straight cochlear ducts, and voluminous sinuses that include a supraocciptal recess, subcondyar sinus, and an anterior tympanic recess that exits the braincase via a prootic fossa. When characters are plotted onto tyrannosauroid phylogeny, there is a twoâstage sequence in which features of the tyrannosauridâstyle brain evolved first (in smaller, nontyrannosaurid species like Timurlengia), followed by features of the tyrannosauridâstyle sinuses (in the first largeâbodied nontyrannosaurid tyrannosauroids like Bistahieversor). This suggests that the signature tyrannosaurid sinus system evolved in concert with large size, whereas the brain did not.Â