FLESHING OUT A LOST WORLD: MID-CRETACEOUS DIVERSITY IN APPALACHIA WITH INSIGHTS FROM THE ARLINGTON ARCHOSAUR SITE

The terrestrial fossil record of Cretaceous aged rocks in North America is very temporally biased. There is a spike in known diversity during the Albian, at the end of the Early Cretaceous, and the latest Cretaceous is comparatively well-sampled, with a high diversity of organisms known from the Campanian and Maastrichtian. However, the stretch of time in between, from the Cenomanian through the Santonian, is very poorly known. Most fossils recovered from this period come from Laramidia to the west, with Appalachia in the east being largely unknown. The Woodbine Formation, in North Texas, represents a rare Appalachian coastal ecosystem with a subtropical and strongly seasonal paleoclimate and evidence of periodic wildfires. Its Cenomanian age positions it within this temporal gap, but until recently fossils known from this deposit were comparatively rare and poorly preserved. New discoveries of well-preserved fossils within the Woodbine Formation, especially at the Arlington Archosaur Site (AAS), are now providing rare insight into the diversity of Appalachian ecosystems during the transition between the Early and Late Cretaceous faunas. At least five taxa of crocodyliform are known from the AAS, representing at least two new species and several distinct ecomorphs. Dinosaurian fossils include the hadrosauroid Protohadros and numerous theropods: an allosauroid, a tyrannosauroid, two dromaeosaurids, and a troodontid. Turtle fossils are also quite diverse, and ongoing screenwashing is revealing a rich microvertebrate assemblage with sharks, bony fish, lungfish, amphibians, snakes, and mammals. Plant microfossils are dominated by ferns with few angiosperms, while macrofossils are largely mid-sized trees, some preserved as charcoal. When compared to other North American Cretaceous deposits, the AAS represents a mixture of groups known from the better-sampled portions of the Early and Late Cretaceous. Geographically, the AAS also records a blend of familiar, Laramidian clades and new taxa, which were endemic to Appalachia. Taken together, the AAS preserves evidence of faunal turnover and evolutionary response to the completion of the Western Interior Seaway, which isolated eastern and western populations and marked the transition between the Early and the Late Cretaceous in North America.