It is divided into the Ahearn Member, the Crazy Johnson Member, and the Peanut Peak Member. Overlying the Peanut Peak Member of the Chadron is the Brule formation, and it is subdivided into the Scenic Member, and the Poleslide Member. Overlying the Poleslide Member of the Brule is the Sharps Formation. Evidence from plant and marine fossils, and oxygen and carbon isotopes indicates that a significant cooling trend began about 50 million years ago and continued through the Oligocene. He determined that the percentage of aquatic taxa was decreasing during this time.
All material is identified, described, and placed in the correct stratigraphic position.
Relative abundance for each taxon over time is based on specimens in the GCVP collection. All measurements were taken with Helios dial calipers to 0.05mm. Pictures of Rhineura floridana and Rhineura hatcherii were taken using a Polaroid model 618091 Microcam, an Olympus 20X binocular dissecting microscope, and a Dazor model 364 flexlight. These images were then scanned into a computer and modified using Adobe Photoshop and Illustrator software. Peltosaurus abbotti is generally accepted as a valid taxon because its skull is greatly convex and its appearance is, as a result, drastically different from that of Peltosaurus granulosus .