Sloths weren't always slow-moving, furry tree-dwellers. Their prehistoric ancestors were huge - up to 4 tons - and when startled, they brandished immense claws. For a long time, scientists believed ...

Thaís Pansani examines the marks humans left on megafauna bones to determine when people arrived in South America and how they interacted with giant mammals Chihiro Kai 14,000 years ago, an early ...