THE FIRST MULTI-TAXA VERTEBRATE ASSEMBLAGE FROM THE MESOZOIC OF ARKANSAS, USA

In the late 1980’s an assemblage of vertebrate remains were discovered at the Briar Gypsum Mine, the site sauropod and theropod tracks from the overlying De Queen Limestone outside of Dierks, Arkansas. The assemblage was discovered in an organic-rich, pyrite-bearing dark grey mudstone interpreted as having been deposited in a lagoonal environment tied to marine facies. Within the assemblage, a diverse fauna of micro and macrovertebrates were discovered. This study describes that assemblage and makes provisional assignments to know taxa from correlative units. Of macrovertebrate remains, elements from a very large theropod are attributed to Acrocanthosaurus atokensis, dermal plates from a large nodosaur-type ankylosaur are attributed to either Pawpawsaurus or Sauropelta, a large ceolognathosuchian crocodile are attributed to Pauluxysuchus, a large solemydid turtle are attributed to Naomichelys speciosa, and remains from a large titanisauriform sauropod are attributed to either Sauroposeidon or Astrophocaudia. The microvertebrate assemblage is dominated by aquatic and semi-aquatic taxa, with an abundance of osteichthyans (Pycnodontiformes, Semionotidae, Amiidae, and Teleostei) and chondrichthyans (Lamniformes and Hybodontidae). Semi-aquatic taxa contain neosuchian crocodylomorphs (Bernissartiidae and Coelognathosuchia, which include Goniopholididae and Pholidosauridae), a solemydid turtle (Naomichelys sp.), and Lissamphibia (Albanerpeton sp.). Terrestrial taxa include indeterminate scincomorphan squamates, dinosaurs (Deinonychus antirrhopus and Richardoestesia sp.), an avian ungual, and a triconodontid mammal tooth. The assemblage is consistent with most of the sparse material documented from Arkansas, namely tracks, but lacks any identifiable material attributable to an ornithomimid, “Arkansaurus,” found in the same region. Combined, the assemblage resembles similar faunas identified from the Trinity Group of Texas and the Antlers Formation of Oklahoma and Texas, but also contains taxa identified from Laramidia (Cloverly and Cedar Mountain formations) and Appalachia (Arundel Formation). The assemblage supports a theme of low diversity for the Early Cretaceous relative to high diversity of the Late Cretaceous, associated with latitudinal climate gradients.