BIOSTRATIGRAPHIC AND GEOGRAPHIC DISTRIBUTION OF CAMARASAURUS (DINOSAURIA, SAUROPODA) FROM THE MORRISON FORMATION

Camarasaurus is one of the most common dinosaurs in the Morrison Formation (Late Jurassic); however, the taxonomy of the three common species, C. grandis, C. lentus, and C. supremus, is still debated. One of the biggest reasons for the debate is that stratigraphic correlation of dinosaur quarries in the Morrison Formation has not succeeded. The stratigraphic distribution of C. grandis and C. lentus overlaps in the upper Morrison Formation; however, C. grandis is concentrated in the upper Salt Wash member, and C. lentus is common in the lower Brushy Basin member. C. supremus is only known from the top of the Brushy Basin member. Likewise, Camarasaurus has three major geographic distributions; C. lentus is found from central Wyoming to central and eastern Utah; C. grandis is commonly known from southern Wyoming to southern Colorado and the northern New Mexico; C. supremus is found in southern Colorado and western Oklahoma. In sauropods, their highly specialized vertebrae are generally one of the most useful elements for their taxonomy, in fact, dorsal vertebrae are the most diagnostic in each species of Camarasaurus. Morphological study of camarasaur dorsal vertebrae suggests that camarasaurs from the northern Morrison (Thermopolis-Cleveland Lloyd quarries) have relatively large centrum; whereas Camarasaurus from the central and southern localities of the Morrison (Dinosaur National Monument-Como Bluff-Garden Park) have relatively small centra and more slender construction of the vertebrae. Both centrum size in dorsal vertebra and the size of the neural spines tend to increase through time in Camarasaurus. These features potentially help to determine stratigraphic position, as well as, correlating dinosaur quarries in the Morrison Formation. The differences in massive vs. slender neural spines in camarasaur dorsals cannot be explained by sexual dimorphism or ontogenetic variation.