A new large-bodied theropod dinosaur from the Upper Morrison Formation (Late Jurassic, Tithonian) of Colorado

DALMAN, S.; PAULINA CARABAJAL, A.; CURRIE, P. J.

Las Vegas

Conferencia; Society of Vertebrate Paleontology Annual Meeting; 2012

Society of Vertebrate Paleontology

In 1953, J. T. Gregory and D. Techter of the Yale Peabody Museum of Natural History discovered a partially preserved theropod skeleton in the Morrison Formation (Late Tithonian) of McElmo Canyon in Montezuma County, Colorado, U.S.A. The specimen consists of several well-preserved cranial, axial, and appendicular elements, some of which are still unprepared and embedded in hard sediment, explaning why this material lay largely unnoticed in the collections of the Museum until now. All the cranial elements, including the braincase, left premaxilla, maxilla, quadratojugal, and dentary were CT scanned so that digital 3D reconstructions could be done, allowing morphological description and comparisons. The McElmo specimen represents a large-bodied theropod, distinct from Allosaurus and Saurophaganax from the same Formation. The specimen is characterized by a short and deep premaxilla (with 4 teeth), deep maxilla, and a robust quadratojugal. These cranial elements are more massive than the equivalent elements in known specimens of Allosaurus. Preliminary phylogenetic analysis, based on previous phylogenies of this clade, positions this new form within Allosauroidea, and more closely to Allosaurus, Fukuiraptor and Neovenator.