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Supporting CT data for: Ontogenetic changes in endocranial anatomy in Gorgosaurus libratus (Theropoda: Tyrannosauridae) provide insight into the evolution of the tyrannosauroid endocranium

Voris, Jared1; Zelenitsky, Darla1; Therrien, François2; Ridgely, Ryan3; Witmer, Lawrence3

Published Dec 08, 2025 on Dryad. https://doi.org/10.5061/dryad.fxpnvx12j

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Abstract

Over the past two decades, increased accessibility to computed tomographic (CT) scanners has allowed researchers to document the endocranium of numerous extinct theropod taxa. However, most of these studies have focused on the morphology of mature individuals. How endocranial morphology might vary through ontogeny in theropods remains largely unknown. Based on CT scans of braincases, we virtually reconstruct the endocranial morphology for a growth series of the tyrannosaurid Gorgosaurus libratus, including two recently discovered juvenile individuals, and compare it to that of other tyrannosauroids.  This study sheds light not only on the ontogenetic changes in endocranial anatomy in a tyrannosaurid but also on the variation in brain morphology among basal coelurosaurs. The endocasts of the smallest Gorgosaurus specimens (~50% adult skull length) exhibit more distinct cerebral hemispheres, optic lobes, and cerebella than do those of larger, more mature specimens. This suggests greater congruence between endocast-to-brain shape among juvenile tyrannosaurids and that their endocasts provide a more accurate representation of the brain than those of adult individuals. The brain morphology of Gorgosaurus is revealed to be intermediate between that of more basal sauropsids (e.g., crocodilians) and derived coelurosaurs (e.g., birds). Plesiomorphic features include large olfactory bulbs and tracts, posteroventrally long axis of the cerebrum, and posterior position optic lobes, whereas derived features include a highly angular brain, somewhat enlarged cerebrum, and a cerebellum that at least partially separates the left and right optic lobes. Future research aiming to establish brain morphology in more basal theropods, such as tyrannosauroids, should consult endocasts of juvenile individuals, as these may more closely reflect the actual brain morphology and could better clarify the nature and timing of changes that led to the evolution of the avian brain.