Birds

Birds (Aves), are a group of reptiles, that are the last living examples of dinosaurs. They are characterized by feathers, bipedal, endothermic, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. They are classed as reptiles under the order Aves with the most living species, at approximately ten thousand, with more than half of these being passerines, sometimes known as perching birds. Birds are the closest living relatives of crocodilians.