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| Labocania aguillonae Rivera-Sylva & Longrich, 2024 Artwork by Andrey Atuchin. |
Abstract
The end of the Cretaceous saw the Western Interior Seaway divide North America into two land masses, Laramidia in the west and Appalachia in the east. Laramidian dinosaurs inhabited a narrow strip of land extending from Mexico to Alaska. Within this geographically restricted area, dinosaurs evolved high diversity and endemism, with distinct species in the north and south. Here, we report a new tyrannosaurid from the Late Campanian-aged Cerro del Pueblo Formation of Coahuila, Mexico, which is part of a tribe of tyrannosaurs originating in southern Laramidia. Phylogenetic analysis recovers the new tyrannosaur as part of a clade including Labocania anomala from the La Bocana Roja Formation of Baja California Norte, Bistahieversor sealeyi from the Kirtland Formation of New Mexico, Teratophoneus curriei from the Kaiparowits Formation in Utah, and Dynamoterror dynastes from the Menefee Formation of New Mexico. Distinct frontal morphology and the younger age (~72.5–73 Ma versus >75.8 Ma for L. anomala) support recognition of the new tyrannosaur as a distinct species of Labocania, Labocania aguillonae. The Labocania clade dominated southern Laramidia at a time when the north was dominated by daspletosaurins and albertosaurines. The high endemism seen in tyrannosaurids is remarkable, given that modern apex predators have large geographic ranges and hints that the diversity of carnivorous dinosaurs has been underestimated.
Keywords: Tyrannosauridae; dinosauria; Campanian; Cretaceous; Laramidia
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| Skeletal reconstruction of Labocania aguillonae (CPC 2974) showing preserved material. Scale = 1 m. |
Systematic paleontology
Dinosauria—Owen 1842
Theropoda—Marsh, 1881
Coelurosauria—von Huene 1914
Tyrannosauridae—Osborn, 1906
Tyrannosaurinae—Osborn, 1906
Teratophoneini—Scherer & Voiculescu-Holvad, 2024
Labocania—Molnar 1974
Labocania aguillonae sp. nov.
Diagnosis: Tyrannosaurine diagnosed by the following character combination (*—autapomorphies): orbit large and circular, with a very strongly convex anteroventral margin of the lacrimal* with a prominent, strongly dorsally extended* subocular process on the lacrimal along the anteroventral margin of the orbit; strong posteroventral extension of the antorbital fossa onto the lacrimal to end below the anterior margin of the orbit; lateral ends of frontals with a very prominent, acutely triangular shape, with strong transversely expanded overlap of frontal onto lacrimal; broad anteromedial extension of supratemporal fossa extending far forward onto frontal*; strong medial projection of postorbitals behind frontals onto dorsolateral surface of postorbital process, such that frontal underlaps the postorbital anteriorly*, lateral teeth with a figure-eight basal cross-section, and deep, prominent grooves or fullers extending from the root up the labial and lingual surfaces of the crown.
Etymology: The species name honors Martha C. Aguillón, discoverer of the specimen and a long-time career paleontologist of Coahuila.
Conclusions:
CPC 2974 represents a new species of tyrannosaurid, Labocania aguillonae, closely related to Labocania anomala, Bistahieversor sealeyi, and Teratophoneus curriei. It adds to the diversity of the Cerro del Pueblo Formation and shows that endemicity existed within tyrannosaurs in the Late Campanian, with distinct species and clades inhabiting the northern Great Plains in the north and the American Southwest and Mexico in the south. Given the limited geographic sampling, many tyrannosaur species likely remain undiscovered. Competition between species likely helped to enforce endemism among dinosaurs. Why large dinosaurs seem to have such unusually high levels of endemism compared to modern mammals remains unclear.
Héctor E. Rivera-Sylva and Nicholas R. Longrich. 2024. A New Tyrant Dinosaur from the Late Campanian of Mexico Reveals a Tribe of Southern Tyrannosaurs. Foss. Stud. 2024, 2(4), 245-272. DOI: doi.org/10.3390/fossils2040012 www.mdpi.com/2813-6284/2/4/12
