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Large numbers of Late Pleistocene bighorn sheep (total counts of identifiable elements: 4,497) Ovis canadensis. are described from the Natural Trap Cave, northern Wyoming. The specimens consist of nearly-intact skulls and enough post-cranial materials to assemble several complete sheep skeletons. Most of the fossils yield radiocarbon dates from 12,000 to 21,000 BP, while the oldest are more than 110,000 years old as dated by the fission-track method on the volcanic ash. The specimens resemble modern bighorn sheep (Ovis canadensis) in having shallow lachrymal fossae and relatively wide rostra. in contrast to the Asian argali (Ovis ammon), which exhibit deep fossae and narrow rostra. The sheep also have a proportionally large body size. A direct ancestor-descendent relationship between modern and the fossil sheep in North America seems probable. Reduction of body size seems likely to have occurred at the end of Pleistocene or the beginning of Holocene time. Young males predominated among the fossil sheep found in the Natural Trap Cave.