Birds are winged, bipedal, endothermic, vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic.
Birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.7 m (8 ft 10 in) Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150-200 Ma (million years ago), and the earliest known bird is the only clade of dinosaurs that survived the Cretaceous-Tertiary extinction event approximately 65.5 Ma.
Many species are of economic importance, mostly as sources of food acquired through hunting or farming. Some species, particularly songbirds and parrots, are popular as pets.
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