New research shows 8,000-pound sloths once dug caves, adapted to oceans, and roamed widely—until climate and humans brought their downfall.

But as the planet cooled again, sloths began to bulk up. The largest ground sloths emerged during the Ice Ages. Big bodies ...

Massive Megatherium sloths once stood as large as Asian elephants, ripping foliage off treetops with prehensile tongues like ...

Researchers analyzed fossils and DNA to get a big-picture view of sloth evolution and determine what drove their immense size ...