Bipedal means walking on two legs. Humans are bipedal creatures: we stand upright and move around on our two feet rather than on four legs like dogs or cats. Birds are also bipedal, hopping and walking on their two legs while using their wings for other purposes.

Scientists believe humans became bipedal millions of years ago, which freed up our hands to carry things, use tools, and eventually build civilizations. This was one of the most important developments in human evolution. Walking upright let our ancestors see farther across the landscape, pick fruit from trees while standing, and travel long distances more efficiently than our four-legged ancestors could.

When dinosaurs walked on two legs, like the Tyrannosaurus rex, paleontologists describe them as bipedal dinosaurs. Some animals can switch between walking on two legs and four: bears sometimes stand bipedal to get a better view or reach something high, even though they normally walk on all fours.