Solving Taphonomic Jigsaw Puzzles: Insight Into the Complex Depositional History of a Lance Formation (Maastrichtian) Dinosaur Bonebed

MCLAIN, Matthew A, Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, mmclain@llu.edu,
CHADWICK, Arthur V, Geology, Southwestern Adventist University, 100 Magnolia, Keene, TX 76059,
BRAND, Leonard R, Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, and
NELSEN, David, Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350.

Rose Quarry, the site of a recently discovered Lance Formation (Maastrichtian) dinosaur bonebed in eastern Wyoming, contains particular taphonomic signatures that suggest a complex history for the formation of the bonebed. The disarticulated, disassociated, and commonly fragmented bones of Rose Quarry are found near the base of a trough-crossbedded sandstone unit along with mudballs and pebbly iron-rich concretions. Some bones are very well-preserved, whereas others possess heavily damaged surfaces. These vast differences in bone preservation, as well as the presence of both whole turtle shells and individual, disarticulated turtle scutes, suggest that Rose Quarry contains a mixed assemblage. Many of the bones (>10%) possess possible tooth marks.

A model is presented to explain these taphonomic features. First, dinosaurs, turtles, and crocodilians died and their carcasses were scavenged. Scavenging dinosaurs may have trampled and crushed bones at this point, creating cracks in bones, which may have resulted in fragmentation during transport. Before weathering of the bones could occur, a flood transported additional bones to the area from a different location. This flood ripped up the bones, organic debris, and mud clasts at the scavenging location. The bones were somewhat abraded before they were finally deposited. The organic debris that was associated with the bones and mud caused numerous iron-rich concretions to form near many of the bones. This taphonomic model for Rose Quarry demonstrates the complexity that may exist for many other vertebrate bonebeds and reemphasizes the importance of careful taphonomic study in the excavation of fossils.

poster presentation at the GSA 2014 meeting, Vancouver, BC, Oct 2014.