Jefferson’s Ground Sloth is one of the most unusual of North American Ice Age mammals. One of several species of sloths that lived in the Western Hemisphere, this one was named to honour U.S. President Thomas Jefferson, who was one of North America’s first palaeontologists. The giant ground sloth originated in South America and moved into North America about 5 million years ago. This sloth is known from Yukon and Alaska fossils 150,000 to 130,000 years old. Jefferson’s Ground Sloth was a longhaired, ox-sized mammal. It was 2.5 to 3 metres long and weighed more than one tonne. Giant sloths were plant-eaters. Their teeth were long, flattened pegs with ridges. Their curved front claws allowed them to hook down high leafy branches from trees. In the Yukon, giant sloth fossils have been found at Old Crow. They became extinct about 9,400 years ago.