TAPHONOMY, TAXONOMY, AND ANATOMY OF SAUROPOD AND THEROPOD DINOSAUR REMAINS FROM THE UPPER JURASSIC MORRISON FORMATION NEAR SHELL, WY

Two quarries near Shell, WY have produced two partial skeletons of sauropod dinosaurs from adjacent stratigraphic horizons. We are currently attempting to decipher the taxonomy, taphonomy, and anatomy of the excavated dinosaur bones. The two quarries differ significantly lithologically and taphonomically. The upper quarry sediment is a silty mudstone from which femur, ribs, vertebrae, and hipbones were excavated, while another femur and vertebrae were uncovered but left to be excavated in future field seasons. Bones excavated from the upper quarry are roughly articulated in original skeletal order. When the first femur was excavated out of the ground, another femur was found directly beneath it. This orientation, and the fairly original skeletal order, suggest that the dinosaur is being uncovered in the articulated state in which it was buried. The upper bone surface of the top femur is collapsed which suggests possible trampling or post-burial compression. The lower quarry sediment is well-cemented sandstone. Vertebrae, ribs, and teeth have been excavated from this site. The bones in this lower quarry are disordered. Theropod teeth were found in the uppermost units yielding bones and were absent in the lower bone-bearing units. The stratigraphically lowest bone-bearing units are associated with extensive thin deposits of coalified plant material. There is no evidence so far that another animal killed the dinosaur; therefore the teeth are possible evidence of scavenging. Since the teeth were only found in the uppermost bone-bearing units, this suggests that only a portion of the skeleton was exposed enough for scavenging. The bones in both quarries were examined using a microprobe for geochemical analyses. The samples from the upper quarry were most likely diagenetically altered by mineralizing solutions that caused some post-depositional changes. Low-temperature minerals such as barite and calcite were found as well as higher levels of sulfur compounds. However, the pores of the lower quarry samples were unmineralized. The role of gypsum and pyrite on samples from both of the quarries will also be explored, as well as the effects of waterlogged environments on bones and the minerals that may or may not develop as a result.