19-5 New Tyrannosaur Material from the Upper Campanian, San Juan Basin of New Mexico Provides Insights into Sympatry and Palate Anatomy of Apex Carnivores in Southern Laramidia

Session: The Campanian Crucible: A synthesis of vertebrate paleobiogeography and ecosystem dynamics in Laramidia

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Abstract:

Tyrannosaurs were among the largest terrestrial carnivores to have ever existed and they dominated the Late Cretaceous ecosystems of Laurasia. Counterintuitively for animals of such scale, the Campanian fossil record shows substantial evidence of provincialism across both North America and Asia among tyrannosauroids and other dinosaurs. This pattern is particularly clear in Southern Laramidia, where most species are known from single formations or depositional basins during the Campanian. Within the San Juan Basin teeth referable to Tyrannosauroidea have been known for decades, however, all diagnostic skeletal material from the Fruitland and Kirtland Formations has previously been identified as Bistahieversor sealeyi. Recent efforts by the NHMLAC to explore the Bisti/De-Na-Zin Wilderness of New Mexico have uncovered new material including a set of remarkably well-preservd cranial bones from a single individual. This new tyrannosaur from the San Juan Basin (Kirtland Fm) is clearly distinguished from B. sealeyi by several features including a smaller, more gracile skull — providing the first evidence of sympatry and potential niche partitioning among tyrannosaurs in Southern Laramidia. Building on the recent recognition of several new genera of tyrannosauroids across New Mexico, Texas, and Utah during the Campanian, we also assess the diversity dynamics and ecological implications for these apex predators based on this new material. Further, the specimen shows fine surface details and intra-sutural tissue which provide a unique opportunity to study the correlations among skeletal and soft-tissue in the tyrannosaur palate. To more completely reconstruct this palate, we collected data on the direct associations among palatal tissues using contrast-enhanced µCT scanning of extant reptiles and birds. Based on these comparisons, we provide the first quantitatively derived estimates of the extent of the soft-tissue of the palatal shelf, the length of the nasopharyngeal duct, and position of the choanae in tyrannosaurs. Taken together, these findings provide key insights into the anatomy and biogeography of these exceptional predators.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4, 2026

doi: 10.1130/abs/2026RM-14330

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