A PALYNOLOGIC PALEOENVIRONMENTAL ANALYSIS OF A DINOSAUR BONE-BEARING BED FROM THE CRETACEOUS HELL CREEK FORMATION, MONTANA

The Cretaceous-age Hell Creek Formation of Montana is the focus of active paleontologic research. Whereas much of this research has been, and continues to be, on the dinosaurs recovered from this formation and how they interacted in social groups, less has been done on understanding the environments in which they lived, particularly in using palynology to make these interpretations. Nineteen palynologic samples were collected from fine-grained beds above and below a dinosaur bone-bearing bed of the Cretaceous-age Hell Creek Formation, Montana. The site, located near the Fort Peck Reservoir, north of Jordan, Montana, was excavated by Dr. Jack Horner for the oldest known (68 m.y.) and best preserved Tyrannosaurus rex skeleton. The stratigraphy of the site indicates a sand-channel lake deposit with a crevasse splay deposit on top that also represents a flood plain environment. Pollen, spores, and algae recovered from the 19 samples indicate the presence of various angiosperms, gymnosperms, seedless vascular plants, mosses and algal cysts. Of the 41 palynomorph species recovered, 35 were attributed to known taxa. Based on counts of 250 palynomorph specimens per slide, gymnosperms were the most abundant group, followed by angiosperms and ferns. Flood plain intervals were identified on the presence of algal cyst species resembling those of modern floating aquatic plants. The surrounding region, determined by pollen and spores deposited within the flood plain environment, was a conifer forest with an undergrowth of ferns and flowering plants.