The Tatman Formation in Wyoming dates to the Wasatchian, within the early Eocene, and preserves fossils from the Ypresian stage. Formed during a time of warm climates and important change in early Cenozoic life, it is known for preserving plant remains as well as other fossils from that interval. Its record contributes to the study of Paleocene and early Eocene diversity in Wyoming, especially in the Bighorn Basin, making it a useful source for understanding ancient life and environmental conditions in the region.