Birds Temporal range:
Scientific classification
Unrecognized taxon (fix):	Aves
Extant Orders
Infraclass Palaeognathae Superorder Struthionimorphae Struthioniformes Superorder Notopalaeognathae Rheiformes Tinamiformes Casuariiformes Apterygiformes Infraclass Neognathae Superorder Galloanserae Galliformes Anseriformes Superorder Neoaves Phoenicopteriformes Podicipediformes Columbiformes Mesitornithiformes Pteroclidiformes Apodiformes Caprimulgiformes Cuculiformes Otidiformes Musophagiformes Opisthocomiformes Gruiformes Charadriiformes Gaviiformes Procellariiformes Sphenisciformes Ciconiiformes Suliformes Pelecaniformes Eurypygiformes Phaethontiformes Cathartiformes Accipitriformes Strigiformes Coliiformes Leptosomiformes Trogoniformes Bucerotiformes Coraciiformes Piciformes Cariamiformes Falconiformes Psittaciformes Passeriformes
Synonyms
Neornithes Gadow, 1883

Birds (Aves) are a group of vertebrates which evolved from dinosaurs. They are endothermic, with feathers.

Modern birds are toothless: they have beaked jaws. They lay hard-shelled eggs. They have a high metabolic rate, a four-chambered heart and a strong yet lightweight skeleton.

Birds live all over the world. They range in size from the 5 cm (2 in) bee hummingbird to the 2.70 m (9 ft) ostrich. They are the class of tetrapods with the most living species: about ten thousand. More than half of these are passerines, sometimes known as perching birds.