includes formations not only in Maryland but also in parts of Washington D. C., Delaware and Virginia. The Arundel Formation was deposited on the edge of the expanding Atlantic Ocean basin. The region preserved in this formation was a broad, and generally flat plain with several streams running across it, probably similar to the modern day coastal regions of Alabama, Georgia, Louisiana and Mississippi. Fossil material assigned to Astrodon has also been found in two Oklahoma localities of the Antlers Formation, which stretches from southwest Arkansas through southeastern Oklahoma and into northeastern Texas. This geological formation has not been dated radiometrically. Scientists have used biostratigraphic data and the fact that it shares several of the same genera as the Trinity Group of Texas, to surmise that this formation was laid down during the Albian stage of the Early Cretaceous Period, approximately 110 mya. The Papo Seco Formation of the Lusitanian Basin in Portugal also provided fossils referred to Astrodon. Paleofauna In what is now Maryland, Astrodon shared its paleoenvironment with dinosaurs such as coelurosaurians, the ankylosaurian Priconodon crassus, the nodosaurid Propanoplosaurus marylandicus, a possible basal ceratopsian, and potentially the ornithopod Tenontosaurus. The fossil evidence points to the presence of the poorly known theropods Dryptosaurus medius, Capitalsaurus potens and Coelurus gracilis, and the well known large theropod Acrocanthosaurus atokensis, which likely were the apex predators in this region. Other vertebrates are not as well known from the formation, but include freshwater sharks, lungfish, at least three genera of turtles including Glyptops caelatus and the crocodyliform Goniopholis affinis. Evidence has shown that the multituberculate early mammal Argillomys marylandensis was also present. Trace fossils included theropod tracks known as Eubrontes and others assigned to the ichnogenus Pteraichinus belonging to a pterosaur, which demonstrate that these animals were present in abundance. The plant life known from this area included trees preserved as silicified wood, cycads like Dioonites, Ginkgo, the ground plant Selaginella and the giant redwood conifer Sequoia. In prehistoric Oklahoma, Astrodon lived alongside other dinosaurs, such as the sauropod Sauroposeidon proteles, the dromaeosaurid Deinonychus and the carnosaur Acrocanthosaurus atokensis. The most common dinosaur in the paleoenvironment preserved in the Antlers Formation is the ornithopod Tenontosaurus. Other vertebrates present at the time of Astrodon included the amphibian Albanerpeton arthridion, the reptiles Atokasaurus metarsiodon and Ptilotodon wilsoni, the crurotarsan reptile Bernissartia, the cartilaginous fish Hybodus buderi and Lissodus anitae, the ray-finned fish Gyronchus dumblei, the