FIELD AND LABORATORY ANALYSES AND DESCRIPTIONS OF PARTIALLY ARTICULATED HADROSAUR FOOT BONES AND SURROUNDING SEDIMENTARY MATRIX AS EXCAVATED FROM A NEWLY EXPOSED BONE BED: LANCE FORMATION EASTERN WYOMING

The preservation quality of the fossils Lance Formation, Late Cretaceous (Maastrichtian) of eastern Wyoming varies widely. Fossils include mummified specimens with soft tissue preservation, articulated skeletons, and disarticulated bones or fragments that may be extremely deteriorated. Few careful attempts have made to explain the conditions that prevailed during the life of the animal, its death, its subsequent burial/depositional environment, or the post depositional and post-lithification environment that resulted in any diagenetic alteration. This newly exposed bone bed afforded the opportunity to analyze geochemical components of bone and adjacent sedimentary materials in-situ with a Niton XRF 3T GOLDD+ field portable analyzer as the excavation proceeded slowly. Materials were examined visually as they were removed and collected. All materials were analyzed in the laboratory for compositional, macroscopic and microscopic details. The area of detailed study was limited to three square feet laterally and twenty inches in depth. Within this area the fluvial channel sequence of depositional facies changed from low energy, deeper quiet water containing abundant plant and microfossil materials in a thin fissile shale, upward to a higher energy silty facies, upward to a thicker medium grained quartz sandstone facies at the top. The in-situ position of the foot bones, the removal of underlying sediments, the water flow and deposition in the upper portion of the channel fill are all indicative of changing conditions in the local environment. Detailed examination of these localized facies change sequences enables a better explanation of environmental conditions as they changed over the relatively brief time required for the living animal to die and become buried. Ultimately, to become fossilized and rest in the lithified strata for some 67 million years. This area was a geochemically hospitable environment for bone preservation once the foot was torn apart, transported and deposited here. It maintained that favorable environment until excavated. No soft animal tissues were found here although fragile plant materials were found in the facies upon which the bones were deposited.