bird fly

Birds (Aves) are a group o endothermic vertebrates, characterised bi feathers, tuithless beakit jaws, the layin o haurd-shelled eggs, a heich metabolic rate, a fower-chaumbered hert, and a lichtweicht bit pure tough skelet. Birds bide warldwide and range in size fae the 5 cm (2 in) bee hummingbird tae the 2.75 m (9 ft) ostrich. Thay rank as the cless o tetrapods wi the maist livin species, at aboot ten thoosand, wi mair nor hauf o thae bein passerines, whiles kent as perching birds or, less richtly, as songbirds.

The fossil record indicates that birds are the lest surviving dinosaurs, termed avian dinosaurs, haed evolved frae feathered ancestors inwith the theropod group o saurischian dinosaurs. True birds erest appeared while the Cretaceous feck, aroond 100 million years aby. DNA-evident shaws that birds diversified dramatically aroond the time o the cretaceous–paleogene extinction event that kilt aff a ither dinosaurs. Birds in Sooth America owercome this event and syne migrated tae ither bits o the warld via multiple laund brigs, while diversifying while periods o global cooling. primitive bird-lik dinosaurs that lie ootdoors cless aves proper, in the broader group avialae, hae bin fun datin back tae the mid-Jurassic period. Mony o thae earlie "stem-birds", sic as archaeopteryx, wur nae yit capable o fully powered flight, and mony keepit primitive characteristics like tuithie jaws in steid o beaks, and lang bony tails.