Revision of the sauropod dinosaurs of the Lower Cretaceous Trinity Group, southern USA, with the description of a new genus

Early Cretaceous sauropods were among the first dinosaurs discovered in North America, but several aspects of their taxonomy and evolution remain poorly understood. Much of this ambiguity stems from lack of anatomical overlap among taxa and the 125-year-long taxonomic confusion surrounding the sauropods Astrodon and Pleurocoelus. New discoveries have begun to remedy the first problem, but a lack of autapomorphies in their holotypes and skeletal associations among their hypodigms renders Astrodon johnstoni, Pleurocoelus altus and Pleurocoelus nanus nomina dubia. Herein I examine the affinities of sauropods from the Trinity Group of Texas and Oklahoma previously referred to as Pleurocoelus' or Astrodon'. Some of this material currently comprises the genera Paluxysaurus and Sauroposeidon from laterally equivalent strata in Texas and Oklahoma, respectively. Although representative individuals of Paluxysaurus are only two-thirds the size of Sauroposeidon, bone histology of Paluxysaurus indicates that the individuals from the type locality were not near adult size. The similar provenance, lack of morphological differences, and shared unique features support referral of Paluxysaurus to Sauroposeidon. Other sauropod remains from the Trinity Group are not referable to Pleurocoelus', Astrodon' or Sauroposeidon. Some of these remains comprise the holotype of Astrophocaudia slaughteri gen. et sp. nov., a basal titanosauriform diagnosed by a hyposphene-hypantrum system in the caudal vertebrae. A sauropod hind limb previously referred to Pleurocoelus' is instead referable to Cedarosaurus weiskopfae based on shared features of the pes. Cladistic analysis indicates that Astrophocaudia and Sauroposeidon are members of Somphospondyli, whereas Cedarosaurus is a brachiosaurid. The Trinity Group of Texas and laterally equivalent Antlers Formation of Oklahoma exhibit similar dinosaur faunas at the generic and specific levels to the Cloverly Formation of Wyoming. This homogeneity with respect to latitude stands in marked contrast to the latitudinal variation in dinosaur communities that developed later in the Cretaceous.