LATE CRETACEOUS DINOSAURS OF THE EASTERN GULF COAST, AND THEIR RELATIONSHIPS WITH ATLANTIC COAST TAXA

Late Cretaceous marine strata of the eastern Gulf Coast (Georgia to Mississippi) yield numerous isolated dinosaur bones and teeth of Santonian and Campanian ages, and a few associated remains. At least one regional species is recognized in each of the following taxa: Tyrannosauroidea, Velociraptorinae, Hadrosaurinae (or possibly derived Iguanodontidae), Ornithomimosauridae, and Nodosauridae. More diversity may be present but the evidence is ambiguous. The best-characterized taxa are the (unnamed) tyrannosauroid and the hadrosaurine, Lophorhothon atopus, which are both basal forms. These seem to be relicts of a pre-Western Interior Seaway immigration before the Cenomanian. Many southeastern dinosaur specimens show association with shark teeth and positive evidence of shark scavenging.

Relationships of Gulf Coast dinosaurs with those in the Upper Cretaceous of the Atlantic Coast (New Jersey to South Carolina) are uncertain because of poor preservation in both regions and significant age disjunctions. All known eastern Gulf Coast dinosaurs are of Santonian and Campanian ages, with the youngest (Demopolis Fm., western AL and MS) from the early-late Campanian. In contrast, few Late Cretaceous dinosaur fossils from the East Coast are older than the mid-Campanian, and most referred specimens are of late Campanian and Maastrichtian age. This age disjunction is compounded by the disappearance of the major coastal predator (the crocodylian Deinosuchus)in the early-late Campanian, which must have profoundly affected dinosaurs along all the Late Cretaceous coasts, as well as the evolution of dinosaurs surviving into the Maastrichtian.