A line of three Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis) cruise the highway in Waterton Park townsite, Alberta, Canada. Wild sheep crossed the Bering land bridge from Siberia during the Pleistocene (about 750,000 years ago) and spread across western North America as far south as Baja California and northwestern Mexico. Genetic divergence from their closest Asian ancestor (snow sheep) occurred about 600,000 years ago.
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