Moabosaurus Utahensis, N. Gen., N. Sp., a New Sauropod from the Early Cretaceous (aptian) of North America

The Early Cretaceous was a time of dramatic change for sauropod dinosaurs in North America. Between the Late Jurassic-aged Morrison Formation and overlying Early Cretaceous strata, there was a dramatic decline in sauropod diversity. Here, we describe a new sauropod that adds to the diversity of the Early Cretaceous, from strata that can be no older than the early Aptian, (125 Ma) some 25 million years younger than the Morrison Formation. Moabosaurus utahensis, n. gen., n. sp., is diagnosed in part by the following suite of characters: axially thin ventral basioccipital with posteriorly sweeping basal tubera; low-spined cervical vertebrae with neural spines that range from shallowly notched on anterior cervical vertebrae to shallow, but widely notched on middle and some posterior cervical vertebrae; posterior cervical and anterior dorsal neural spines with extremely low, axially thin, laterally wide ridges at the level of the zygapophyses; some cervical ribs with bifid posterior shafts; anterior and posterior caudal vertebrae with strongly procoelous centra, middle caudal vertebrae with mildly procoelous centra, and distal caudal vertebrae with moderately-to-strongly procoelous centra. To determine the phylogenetic position of Moabosaurus we utilized three different datasets and performed four analyses. All results are in agreement that Moabosaurus is a neosauropod. The two most resolved trees indicate it is a macronarian, specifically a basal titanosauriform. The thick-walled, camerate presacral vertebrae and other characters, however, preclude a more highly nested position of Moabosaurus within either Titanosauriformes, which is characterized by moderately camellate presacral vertebrae, or Somphospondyli, which is characterized by fully camellate presacral vertebrae, including the neural arches. Incorporation of these and other characters, particularly those shared with Turiasaurus and Tendaguria, into phylogenetic analyses will help resolve the interrelationships of Moabosaurus with other neosauropods. 1Museum of Paleontology, Department of Geological Sciences, S389 ESC, Brigham Young University, Provo, Utah 84602, U.S.A. (brooks_ [email protected]; [email protected]) 2Department of Biology, 4142 LSB and M. L. Bean Museum, Brigham Young University, Provo, Utah 84602, U.S. A. (michael_whiting@ byu.edu) 3College of Veterinary Medicine, 1130 Wire Road, Auburn University, Auburn, Alabama 36849, U.S.A. ([email protected]) 190 b. b. britt et Al.