Birds, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at approximately ten thousand. The fossil record indicates that birds are the last surviving group of dinosaurs, having evolved from feathered ancestors within the theropod group of saurischian dinosaurs.
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Last updated: 20/01/2017
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