NEW DATA ON MID- CRETACEOUS ECOSYSTEMS AND FAUNAL DIVERSITY IN APPALACHIA: INSIGHTS FROM THE WOODBINE FORMATION (CENOMANIAN) OF NORTH TEXAS

The terrestrial record of the mid-Cretaceous (Aptian to Santonian) in North America remains poorly known. Discoveries in the western United States provide a detailed record of vertebrate diversity and ecosystem dynamics for Laramidia, including a poorly understood faunal transition. However, little is known of terrestrial communities from the early Late Cretaceous of Appalachia, which is critical in reconstructing the complex biogeographic and evolutionary forces that drove the reorganization of these Late Cretaceous terrestrial ecosystems. The Woodbine Formation in north central Texas has been dated to middle to late Cenomanian (95-100 mya) placing it within the sparsely sampled middle Cretaceous interval. Deposited within an extensive deltaic system on the southwestern margin of Appalachia, the site provides a window into the diversity of this poorly understood landmass. Recently, multiple localities within the Woodbine have yielded an extraordinarily diverse terrestrial and coastal assemblage including plants, sharks, bony fishes, lungfish, turtles, amphibians, mammals, crocodyliforms, birds, and dinosaurs, providing a unique glimpse into this marginal marine ecosystem. Of particular interest is the high diversity of predators now recognized within this group. At least four crocodyliform taxa have been identified based on cranial and post cranial remains that represent multiple ecomorphs from semi-aquatic, ambush predators to fully marine taxa. In addition, new theropod material, including isolated teeth, postcranial remains, and footprints, have been attributed to an allosauroid, a tyrannosauroid, a large dromaeosaurine, smaller dromaeosaurids, a troodontid, and a caenagnathid. The Woodbine fauna demonstrates similar taxonomic composition to contemporaneous deposits in Laramidia, while including groups previously undocumented in Appalachia. This faunal assemblage is characterized by Early Cretaceous groups mixing with basal representatives of Late Cretaceous communities, documenting a faunal turnover similar to that seen in Laramidia. Preliminary work shows a differential response among taxonomic groups in the Woodbine Formation, suggesting a unique strategy to isolation and beginning divergence of faunas on each side of the Western Interior Seaway.