DELTA PLAIN ENVIRONMENTS AND ECOLOGY OF THE CRETACEOUS (CENOMANIAN) WOODBINE FORMATION AT THE ARLINGTON ARCHOSAUR SITE, NORTH TEXAS

The Arlington Archosaur Site is a diverse fossil locality occurring within the Cretaceous (Cenomanian) Woodbine Formation of North Central Texas that preserves a coastal ecosystem along an inundated delta plain. The site preserves multiple components of the coastal system with the base section consisting of a peat bed. The peat contains crocodile remains from a new species of crocodilian along with plant mesofossils and logs. The new crocodile is represented by crania, post crania and osteoderms. The logs are carbonized and vary from 2-4m in length, representing a low growth coastal mangrove. Overlying the peat is a fossil horizon containing remains of vertebrates in a mudstone. The mudstone is mottled and rooted, indicative of pedogenesis along an inundated delta plain paleosol horizon. The vertebrates occurring within this horizon include dinosaur (ornithopod & theropod), crocodile, chelonian and dipnoan. A new lungfish is represented by pterygopalatine and prearticular tooth plates. Overlying the fossil bearing horizon is a heavily rooted Histic Gleysol, typical of coastal wetland soil formation. Additional ecological data at the site, >100 coprolites recovered demonstrate a variety of morphologies suggestive of multiple coastal taxa. The morphologies are cylindrical, spiral and ovoid. Cylindrical coprolites are indicative of crocodilian intestinal tract material. Spiral coprolites have a pronounced spiral that coils to the end; isopolar and amphipolar. Spiral coprolites are indicative of brackish marine taxa; shark and fish. Large, ovoid coprolites are interpreted as dinosaur based on size and the presence of plant remains. All coprolites recovered are preserved intact, indicating rapid burial in a low energy environment. The geologic and fossil data recovered from the Arlington Archosaur Site represents a unique window view into the Cenomanian coastal ecosystems of North America.