Though we think of dinosaurs as being extinct, recent research suggests that their modern relatives live among us in the form of birds. Like birds, many dinosaurs built nests, laid eggs, and had feathers. Over the last twenty years, scientists have collected more and more evidence suggesting that dinosaurs evolved into birds. For example, thousands of fossils of dinosaurs with feathers have been found in China, and fossilized dinosaur eggs are similar in size and shape to birds' eggs. Fossils have also revealed information about dinosaurs' skeletons. Birds have hollow bones to enable flight, and so did some dinosaurs. In addition, birds and dinosaurs exhibit many similarities in their legs, feet, and claws. What is the main idea of the passage?