Long before today’s tree-dwelling sloths, a 4-ton giant roamed South America — and it may have stood and fought like a bear.

Sloths appear defenseless, slow, and vulnerable in ecosystems filled with predators. Yet despite these disadvantages, they persist in environments where speed usually determines survival. Scientists ...

Sloths make modern life look exhausting. While the rest of the world rushes around, these tree-dwellers adhere to a simple routine that has been effective for millions of years. Behind their sleepy ...