Abstract:   Polecat Bench and McCullough Peaks in the northern Bighorn Basin of Wyoming have yielded major discoveries leading to understanding both mammalian biostratigraphy of the North American Paleocene, and the pattern and cause of continental faunal turnover at the Paleocene-Eocene thermal maximum. In 1910, Princeton and American Museum paleontologists showed that mammals of the Paleocene were distinctly different from those of the Eocene. This soon led to acceptance of the Paleocene as an epoch different from the Eocene. Eighty years later, Michigan and Carnegie Institution paleontologists showed that the continental Paleocene-Eocene boundary was marked by abrupt faunal turnover and dwarfing associated with a major carbon isotope excursion. This led to recognition of the Paleocene-Eocene thermal maximum or ‘PETM’ as a greenhouse warming event that was truly global. A young scholar involved in paleontology in 1950, Minchen Chow, was introduced to field work on Paleocene mammals in Wyoming. There he developed the experience and expertise that led to parallel exploration of the Paleocene in China. The challenge now is to understand how the parallel Paleocene histories of the North American and Asian continents fit together.