Birds have colonized every environment on Earth, and they come in an astonishing variety of shapes, colors, and sizes. There are more than 10,000 species of bird alive today, so how did they come to be everywhere and so diverse?

Scientists began understanding the evolutionary history of birds with the discovery of a dinosaur fossil called Archaeopteryx in Germany in the 1860's. It was clearly an ancient bird, but with its distinct claws, tail, and toothed beak, it also had dinosaur features. It led naturalists to a sensational theory: that birds must have evolved from dinosaurs. But it took another century to clinch the case with another spectacular fossil, Deinonychus. It was a dinosaur with many features of birds, including one that all birds have today: a wishbone. With these two milestone discoveries, and the recent unearthing of bird-dinosaur fossils in China, scientists have a clearer picture of the evolution of birds and evidence confirming that they evolved from dinosaurs.