The first reported ceratopsid dinosaur from eastern North America (Owl Creek Formation, Upper Cretaceous, Mississippi, USA)

Résumé de l'étude:

Ceratopsids (“horned dinosaurs”) are known from western North America and Asia, a distribution reflecting an inferred subaerial link between the two landmasses during the Late Cretaceous. However, this clade was previously unknown from eastern North America, presumably due to limited outcrop of the appropriate age and depositional environment as well as the separation of eastern and western North America by the Western Interior Seaway during much of the Late Cretaceous. A dentary tooth from the Owl Creek Formation (late Maastrichtian) of Union County, Mississippi, represents the first reported occurrence of Ceratopsidae from eastern North America. This tooth shows a combination of features typical of Ceratopsidae, including a double root and a prominent, blade-like carina. Based on the age of the fossil, we hypothesize that it is consistent with a dispersal of ceratopsids into eastern North America during the very latest Cretaceous, presumably after the two halves of North America were reunited following the retreat of the Western Interior Seaway.

Eastern dinosaurs

Non-avian dinosaurs from Cretaceous deposits in the eastern US have been well publicized (Weishampel & Young, 1996; Schwimmer, 1997). Although few discoveries are complete enough for comprehensive description and precise taxonomic assignment, recent notable exceptions include a tyrannosauroid and hadrosaurid from Alabama (Carr, Williamson & Schwimmer, 2005; Prieto-Márquez, Erickson & Ebersole, 2016a, 2016b). Cretaceous dinosaur finds from eastern North America are not rare, but they are infrequent. Since Cretaceous dinosaur remains were first reported on the east coast in the 1850s, numerous specimens representing several groups, both ornithischian and theropod, have been reported from Mississippi to New Jersey. Most of this material consists of isolated and often fragmentary elements, like the ceratopsian tooth reported herein. Collectively, however, the scattered discoveries across the Gulf and Atlantic Coastal Plain reveal an eastern North American Cretaceous dinosaur bestiary that included six major dinosaur clades. To date, these include hadrosauroids (Langston, 1960; Prieto-Márquez, Weishampel & Horner, 2006; Prieto-Márquez, Erickson & Ebersole, 2016a), ankylosaurians (Langston, 1960; Weishampel & Young, 1996; Stanford, Weishampel & Deleon, 2011), tyrannosauroids (Baird & Horner, 1979; Schwimmer et al., 1993; Carpenter et al., 1997; Carr, Williamson & Schwimmer, 2005), dromaeosaurids (Kiernan & Schwimmer, 2004), ornithomimids (Baird & Horner, 1979; Carpenter, 1982; Schwimmer et al., 1993), and ceratopsians (Chinnery et al., 1998; Longrich, 2016; this paper).

Conclusion

The ceratopsid tooth from the Owl Creek Formation of Mississippi represents the first unequivocal occurrence of this clade in Appalachia (eastern North America). The fossil is consistent with the hypothesis that clades from Laramidia (western North America) dispersed eastward during the retreat of the Western Interior Seaway sometime during the Maastrichtian. We predict that future work will uncover additional evidence of “western” vertebrate clades in Appalachia; in particular, careful placement within a geological context will help to establish the exact timing and tempo of the seaway retreat.