NEW CROCODYLOMORPH MATERIAL REFERABLE TO BRACHYCHAMPSA CF. SEALEYI AND AND CF. DENAZINOSUCHUS FROM THE MENEFEE FORMATION OF NEW MEXICO AND CROCODYLOMORPH ECOLOGY IN MIDDLE CAMPANIAN SOUTHERN LARAMIDIA

We report a small, fragmentary crocodylomorph skull, WSC 16509, from the Upper Cretaceous (middle Campanian) Allison Member of the Menefee Formation, New Mexico, USA. WSC 16509 closely matches anatomical features of UCMP 133901 (a referred specimen of the alligatoroid Brachychampsa montana from the Maastrichtian Hell Creek Formation of North Dakota), including a sagittal ridge extending rostrocaudally along the ventral surface of the basioccipital and the large, convex condyle on the lateral part of the mandibular articulation on the quadrate. The genus Brachychampsa has been known from the Allison Member since 1996, with the description of NMMNH P-25050, the holotype partial skull of B. sealeyi. This species was diagnosed by characters pertaining to the rostrum and maxillary teeth, and while these elements are not preserved in WSC 16509, its occurrence in the Allison Member supports a tentative designation as Brachychampsa cf. sealeyi. Three additional crocodylomorph specimens from the Allison Member (WSC 10610, UMNH VP 28349, WSC 16603) are identified as cf. Denazinosuchus which exhibit subrectangular shape, thin cross-sectional width, large irregular pits, and lack of keel. As we described a specimen of the much larger alligatoroid Deinosuchus in 2021, there are now three distinct crocodylomorphs known from the Allison Member. Brachychampsa, Deinosuchus, and material resembling Denazinosuchus have also been reported from the Kaiparowits Formation of Utah as well as the Fruitland Formation of New Mexico, stratigraphically higher in the San Juan Basin from the Menefee Formation, suggesting a complex ecology spread out over southern Laramidia during the middle Campanian. Niche partitionings among crocodylomorphs might have been driven by diet, as Deinosuchus has been interpreted as preying upon large terrestrial vertebrates, while the bulbous dentition and dentary morphology of the much smaller Brachychampsa might indicate a preference for armored prey.