File:Tympanuchus phasianellus (sharp-tailed grouse).jpg

English: Tympanuchus phasianellus (Linnaeus, 1758) - sharp-tailed grouse (mount, Field Museum of Natural History, Chicago, Illinois, USA).

Classification: Animalia, Chordata, Vertebrata, Aves, Galliformes, Phasianidae

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Birds are small to large, warm-blooded, egg-laying, feathered, bipedal vertebrates capable of powered flight (although some are secondarily flightless). Many scientists characterize birds as dinosaurs, but this is consequence of the physical structure of evolutionary diagrams. Birds aren’t dinosaurs. They’re birds. The logic & rationale that some use to justify statements such as “birds are dinosaurs” is the same logic & rationale that results in saying “vertebrates are echinoderms”. Well, no one says the latter. No one should say the former, either.

However, birds are evolutionarily derived from theropod dinosaurs. Birds first appeared in the Triassic or Jurassic, depending on which avian paleontologist you ask. They inhabit a wide variety of terrestrial and surface marine environments, and exhibit considerable variation in behaviors and diets.