Ten Years Excavation at an Extensive Lancian Edmontosaurus Bonebed in Northeastern Wyoming

TURNER, Lawrence, Dept. of Mathematics and Physical Sciences;
CHADWICK, Arthur, Dept. Biology, Southwestern Adventist University, Keene, TX  76059; and
SPENCER, Lee, Dept. Biology, Southern Adventist University, Collegedale, TN.

We have been working for ten years in an extensive Edmontosaurus bonebed in eastern Wyoming in the Upper Cretaceous Lance Formation. Our application of high-resolution GPS technology has enabled us to maintain precise positional information on all recovered objects. We have been able to reconstruct virtual quarries with centimeter accuracy in the computer using GIS software and field photographs of the bones. Although we have only examined a small percentage of the total extent of the deposit in detail, test quarries in remote areas have afforded an opportunity to evaluate the deposit as a whole. Based on excavation of 500 of an estimated 250,000 square meters of bonebed in ten localities, we estimate the deposit contains the remains of more than 10,000 animals. The disarticulated bones appear pristine, exhibiting little evidence of weathering or abrasion. The association of numerous shed theropod teeth suggests scavenging occurred prior to final transport and burial.

The bonebed was deposited with a matrix of clay as a normally graded bed, possibly from a debris flow in relatively deep water. Contact with an overlying fine grained immature sandstone is sharp and flat. Extensive dewatering structures in the sandstone are consistent with rapid accumulation of these sediments. We are suggesting that an unknown catastrophe, perhaps volcanic in nature resulted in the rapid extinction of a large number of mature animals, whose carcasses accumulated on a shoreline where scavenging, rotting and disarticulation took place. Subsequent remobilization of the fetid mass, along with the sediments encasing the bones, perhaps triggered by local or regional tectonics resulted in transport for an undetermined distance into deeper water where they were finally buried in a meter thick, normally graded bed.

poster presented at SVP 2010 meeting, Pittsburgh, PA, Oct 2010