At the Crossroads of the Cretaceous: The Woodbine Group and Understanding the Evolution of Appalachian Continental Ecosystems in the Late Cretaceous
NOTO, Christopher R; University of Wisconsin-Parkside, Kenosha, WI. ADAMS, Thomas L; Witte Museum, San Antonio, TX. DRUMHELLER, Stephanie K; University of Tennessee-Knoxville. ADRIAN, Brent; Midwestern University, Glendale, AZ. SMITH, Heather F; Midwestern University, Glendale, AZ. GROSSMAN, Ari; Midwestern University, Glendale, AZ.
The most extensive records of Cretaceous terrestrial and near-coastal vertebrate fossils in North America occur in Lower Cretaceous (Aptian-Albian) and Upper Cretaceous (Campanian-Maastrichtian) strata. The intervening 20 million years (Cenomanian-Santonian) separating these records spans a period of major faunal turnover that remains poorly known. To date, almost all fossils documenting this transition derive from Laramidia while Appalachian fossils remain scarce. One Appalachian fossil assemblage, from the Woodbine Group of north-central Texas, provides important information about the middle-late Cenomanian continental ecosystems of Appalachia early in this transition. The Woodbine assemblage contains over 40 vertebrate taxa including sharks, bony fishes, lungfish, turtles, snakes, amphibians, mammals, crocodyliforms, birds, and dinosaurs, as well as plants and invertebrates, from multiple localities deposited within an extensive deltaic system. Predatory species include four crocodyliforms, several aquatic turtles representing multiple ecomorphs, and a large size range of theropods including an allosauroid, tyrannosauroid, dromaeosaurid, troodontid, and caenagnathid. Herbivores are less diverse, represented only by the large-bodied hadrosauroid Protohadros and an early nanhsiungchelyid turtle. The Woodbine fauna provides the first record of multiple taxa on Appalachia. This assemblage is similar both in terms of ecological diversity and taxonomic composition to contemporaneous deposits in Laramidia, sharing multiple, phylogenetically close relatives. These links support the presence of a more cosmopolitan North American fauna shared between the two landmasses prior to completion of the Western Interior Seaway (WIS). The Woodbine faunal assemblage mixes Late Jurassic and Early Cretaceous groups with basal representatives of Late Cretaceous communities. The assemblage combines Laurasian and Gondwanan forms, Asian and European migrants, and endemic taxa. Preliminary work shows a faunal transition similar to Laramidia was underway in Appalachia by the middle Cenomanian, likely starting before the WIS was complete. However, adaptations by taxa of the Woodbine suggest a unique response to changes in local conditions created by the separation of Larimidia and Appalachia, leading to the evolution of divergent faunas on either side of the recently completed WIS.