“Here be Dragons”: Shed Teeth Potentially Indicate the Presence of Multiple Unidentified Allosauroids from the Early Cretaceous Cedar Mountain Formation of Utah

Allosauroids were apex predators in many terrestrial ecosystems from the Early to early Late Cretaceous. Despite this, the only formally described allosauroid taxa from Cretaceous North America are Acrocanthosaurus of the Antlers Formation of Oklahoma, and the highly fragmentary Siats from the Cedar Mountain Formation of Utah. This lack of known allosauroids is especially apparent in the Yellow Cat Member of the Cedar Mountain Formation, based on the rarity of reported bones and absence of named taxa. However, their presence has previously been inferred by shed teeth from the lower portion of the Yellow Cat. Here we report on likely allosauroid teeth from three localities, Grayash, Blane II, and Doelling′s Bowl, in the Yellow Cat Member of the Cedar Mountain Formation, the former two localities being in the upper portion of the Yellow Cat which until now has not produced any allosauroid remains, at least not any reported in scientific literature. We also assess teeth tentatively identified as Acrocanthosaurus from the Long Walk Quarry in the Ruby Ranch Member of the Cedar Mountain Formation, and the Sonorasaurus Quarry in the Turney Ranch Formation of Arizona. Principal component analysis of linear and geometric morphometrics supports these teeth as being from allosauroids and specifically within Carcharodontosauria, making the Yellow Cat teeth the earliest reported evidence of carcharodontosaurs in North America. Furthermore, their co-occurrence with Utahraptor confirms that multiple large predators lived in this environment and suggests that North American allosauroids did not yield the entire predatory niche to other theropods until their extinction in the Cenomanian-Turonian ages. Lastly, the teeth from the different Yellow Cat Member localities appear morphometrically distinct from each other, suggesting that each may represent a different taxon, though small sample size prohibits a definitive statement on this. While the Arizona Acrocanthosaurus tooth may belong to a species of Acrocanthosaurus, the Long Walk teeth differ from Acrocanthosaurus atokensis in having significantly lower denticle density, and may represent a new taxon. We conclude that there may be as many as four carcharodontosaurid theropod taxa in the Cedar Mountain Formation, thus, the diversity of allosauroids in Early Cretaceous North America is likely greater than previously recognized.