Birds

Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals. Around 10,000 living and recently (after 1500) extinct species of birds compose the class Aves, making them the most diverse tetrapod vertebrates. They inhabit ecosystems across the globe, from Arctic terns to Antarctic penguins. Birds range in size from the tiny hummingbirds to the huge Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, c 200 to 150 Ma (million years ago), and the earliest known bird is the Late Jurassic