CHARACTERISTICS OF MAJOR FOSSIL VERTEBRATE LOCALITIES IN THE WIND RIVER FORMATION (EOCENE), WIND RIVER BASIN, WYOMING

During the summer of 2010, the Teen Science Scholars at the Denver Museum of Nature & Science explored the Wind River Formation for fossil plants and vertebrates in the Wind River Basin, Wyoming (Eocene). From the 16 localities visited more than 500 specimens were found. Two localities were especially fossiliferous: the “Buck Spring Quarries” (DMNS 115) and “Sullivan Ranch” (DMNS 58). DMNS 115 contains fossils dating from the latest Wasatchian Land Mammal Age (LMA, Wa-7), while DMNS 58 contains specimens from the earliest Bridgerian LMA (Br-1a). The localities were compared geologically and paleoecologically. Mineral composition of the fossiliferous rocks preserving the fossils was very similar, with high traces of calcium carbonate in the mudstone, making fossil preservation high for bones, teeth and shells. The main fossil bed at DMNS 115 is a gray mudstone and that at DMNS 58 is a red mudstone. A dark maroon shale layer at DMNS 115 can be used to trace the fossil beds stratigraphically. Both localities are extremely fossiliferous, and are known for providing a diverse fauna. The 2010 data suggests that DMNS 115 has at least 28 different species (73 specimens) and DMNS 58 has at least 30 different species (113 specimens). Previous records suggest DMNS 115 has over 64 species of mammals and DMNS 58 has over 80 species. DMNS 115 contains Lambdotherium specimens, which is the index fossil for Wa-7. DMNS 58 lacks specimens of Lambdotherium, but contains specimens of Eotitanops, which is the index fossil for Br-1a. This data confirms previous studies indicating that the DMNS 115 is older than DMNS 58. The most significant fossil discoveries include a new lizard skull, a new species of artiodactyl, and the first associated upper and lower jaws of Absarokius sp., cf. A. witteri.