Feisty young Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis) climb a road cut along Bow Valley Parkway, Banff National Park, 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. The Canadian Rocky Mountain Parks World Heritage Site was declared by UNESCO in 1984.
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