BIRDS
Birds evolved from dinosaurs—not once, but probably multiple times—during the Mesozoic Era, and today they are by far the most prolific flying vertebrates, numbering about 10,000 species spread across 30 separate orders. Birds are characterized by their coats of feathers, their warm-blooded metabolisms, their memorable songs (at least in certain species), and their ability to adapt to a wide range of habitats—witness the ostriches of the Australian plains and the penguins of the Antarctic coastline. For more, see 10 Facts About Birds and The 30 Main Bird Groups.
