TAPHONOMY OF THE MYGATT-MOORE QUARRY, A LARGE DINOSAUR BONEBED IN THE UPPER JURASSIC MORRISON FORMATION OF WESTERN COLORADO

The Late Jurassic age Mygatt-Moore Quarry is located in the middle Brushy Basin Member of the Morrison Formation. Located in western Colorado, this quarry has been worked since the early 1980s, producing a large sample of fossil vertebrate material consisting mostly of dinosaurs. For this study, 796 identifiable bones were counted from the Museum of Western Colorado's collections with the goal of characterizing the vertebrate fauna from this site for the first time. The bone sample consists of 50% sauropod bones and 30% theropod. A minimum number of 21 individual dinosaurs are represented. The most abundant taxon at the quarry is the theropod Allosaurus (29%), which is represented by 233 skeletal elements indicating a minimum of 6 individuals (5 adults, 1 juvenile); in addition, more than 190 mostly shed teeth of Allosaurus have been recovered from the site. The sauropod Apatosaurus is next most abundant (20%) with 160 elements representing 5 individuals (3 adults, 1 sub-adult, 1 juvenile). Approximately 19% of the sample consists of bones of the ankylosaur Mymoorapelta, mostly osteoderms and lateral spines (2 individuals). The three most abundant sauropods in the Morrison Formation (Camarasaurus, Apatosaurus, and Diplodocus) also are preserved at the Mygatt-Moore Quarry, but unlike within the formation as a whole, at the MMQ Apatosaurus accounts for 85% of the sauropod bones at the site; in the formation overall, Camarasaurus is the most abundant sauropod. Voorhies transportation group analysis of the sauropod bones suggests that the Mygatt-Moore sample is a mixed assemblage dominated by neither transportable nor lag groups (I nor III). Numerous bones were freshly broken before burial and several contain theropod tooth marks, while some bone fragments are highly rounded. Turtle and crocodilian material is extremely rare, and fish are unknown from the main bone layer. These data are consistent with the interpretation that the MMQ represents an ephemeral, overbank deposit with only intermittent hydraulic influence.