Some birds, especially corvids and parrots, are among the most intelligent animal species a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.Ĭhambers 20th Century Dictionary (0.00 / 0 votes) Rate this definition:īėrd, n. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Flightless birds include ratites, penguins, and a number of diverse endemic island species.
Wings are evolved forelimbs, and most bird species can fly. All living species of birds have wings the most recent species without wings was the moa, which is generally considered to have become extinct in the 16th century. Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Paleontologists regard birds as the only clade of dinosaurs to have survived the Cretaceous–Paleogene extinction event 66 million years ago. The fossil record indicates that birds emerged within theropod dinosaurs during the Jurassic period, around 150 million years ago. Extant birds range in size from the 5 cm Bee Hummingbird to the 2.75 m Ostrich. All present species belong to the subclass Neornithes, and inhabit ecosystems across the globe, from the Arctic to the Antarctic. With around 10,000 living species, they are the most speciose class of tetrapod vertebrates.
Freebase (0.00 / 0 votes) Rate this definition:īirds are feathered, winged, bipedal, endothermic, egg-laying, vertebrate animals.