Amphibian, reptilian, and avian remains from the Fox Hills Formation (Maastrichtian): Shoreline and estuarine deposits of the Pierre Sea in south-central North Dakota

Abstract

Although vertebrate fossils, except for fish, are not common in the Maastrichtian Fox Hills Formation, amphibian, reptilian, and avian remains have been recovered at several localities in south-central North Dakota from shoreline facies of the retreating Pierre–Fox Hills seaway. This mixed fauna of aquatic, terrestrial, and marine taxa provides insight into the composition of coastal communities and habitats at the interface between the Hell Creek delta and the Western Interior Seaway. The delta-platform aquatic paleocommunity is represented by the efficient swimming salamanders Opisthotrition kayi and Lisserpeton bairdi, the carnivorous soft-shelled turtle “Aspideretes” sensu lato, the underwater piscivorous predator Champsosaurus laramiensis, and the large, predatory crocodile ?Borealosuchus. Terrestrial areas were inhabited by the tortoise-like Basilemys and the predatory dinosaurs Tyrannosaurus and cf. Saurornitholestes. Birds occupied niches in the warm-temperate to subtropical, forested delta platform and shoreline areas. These nonmarine taxa in the Fox Hills Formation indicate that the geographic range of these animals extended to shoreline areas of the Western Interior Seaway. The toxochelyid turtle Lophochelys and the ambush predators Mosasaurus dekayi and ?Plioplatecarpus resided in the shallow marine and estuarine habitats. These taxa and marine fish taxa reported earlier indicate that normal marine conditions in southcentral North Dakota persisted into the latest Late Cretaceous in comparison with coeval Hell Creek Formation sites more distal from the Western Interior Seaway.