Smithsonian Contributions to Paleobiology, no. 98, viii+102 pages, frontispiece + 52 figures, 1 appendix with 13 tables, 2016. — Patriomanis americana is the only pangolin (Mammalia, Pholidota), living or extinct, known from the Western Hemisphere. It derives from latest Eocene (Chadronian North American Land Mammal Age) deposits from central Wyoming and western Montana. Since its initial description more than 40 years ago based on a partial skeleton, several nearly complete skeletons have been discovered, together including nearly every bone in the skeleton. This taxon is thus not only the most completely preserved fossil pangolin but is also among the best preserved of any Eocene mammal taxon. In the present study we have prepared a detailed, bone-by-bone description of the osteology of Patriomanis, comparing it with other well-known fossil pangolin skeletons (Eomanis, Euromanis, Cryptomanis, and Necromanis), as well as representatives of the three extant pangolins genera (Manis, Smutsia, Phataginus). We provide a catalog of all known Patriomanis specimens and their provenance and an extensive series of measurement tables incorporating the comparative taxa. We analyze the alpha-level taxonomy of the genus, concluding that all specimens should be kept in a single species, Patriomanis americana, based on currently available fossil material. We summarize the taxonomic and phylogenetic position of Patriomanis and discuss its implications for the biogeographic history of the order Pholidota. We analyze the paleobiology of Patriomanis, concluding that it was likely a myrmecophagous, arboreal animal with a prehensile tail. Last, we discuss its paleoecology, suggesting that its late appearance in the Eocene record, during a time of global cooling, may imply that earlier pangolins are waiting to be discovered in the Eocene record of Asia and North America. KEY WORDS: Eocene, fossils, morphology, osteology, pangolins, Patriomanis, Pholidota, skeleton, skull.