TAPHONOMY OF THE AARON SCOTT QUARRY, UTAH (MORRISON FORMATION, JURASSIC)

The Aaron Scott Quarry is an important accumulation of Jurassic fauna within the Morrison Formation in central Utah. Although the Morrison Formation is well known for its dinosaur fauna, having produced type specimens of several well known species, the Aaron Scott Quarry hosts, with the dinosaurs, an abundance of microfauna including crocodiles, sphenodontia, and possibly mammals. Dinosaur specimens are dominated by Diplodocus and Apatosaurus but also include Allosaurus, Ceratosaurus and Othneilla. Taphonomical analysis is used to understand how this diverse fauna accumulated.

The bone horizon consists of a silty sandstone overlain by a silty mudstone. Within the sandstone, sauropod remains are dominated by partially articulated cervical and caudal segments while isolated teeth dominate the carnivore remains. Individual bones and articulated segments trend southwest and are approximately horizontal.

Stratigraphic analysis indicates that the bones were deposited in a lowstand systems tract of a lacustrine delta, with the delta prograding to the west. The high diversity of the fauna supports a near-shore delta plain environment, where food and water are abundant. A southwest lineation of the bones indicates alignment of the bones due to current, possibly within a distributary channel. Although the bones show lineation, partial articulation and the concentration of vertebral elements indicates that the bones had not been transported a great distance prior to deposition. Animals may have died along the shore of a lake to the west, possibly as a result of predation by Allosaurus and Ceratosaurus. Predation destroyed the meaty part of the body, leaving behind the less appetizing neck and tail. Following a short period of desiccation, carcasses accumulated in the distributary channel and became preferentially aligned toward the lake due to fluvial currents. Raising water levels subsequently submerged the bones, where silty mudstone buried them.