Bats fly, whales swim, gibbons swing from tree to tree, horses gallop, and humans swipe on their phones—the different habitats and lifestyles of mammals rely on our unique forelimbs. No other group of vertebrate animals has evolved so many different kinds of arms: in contrast, all birds have wings, and pretty much all lizards walk on all fours. Our forelimbs are a big part of what makes mammals special, and in a new study in the Proceedings of the National Academy of Sciences, scientists have discovered that our early relatives started evolving diverse forelimbs 270 million years ago—a good 30 million years before the earliest dinosaurs existed.
