page_title: Evolution of birds
section_title: Classification of modern species
hierarchical_section_title: Evolution of birds / Classification of modern species
caption_attribution_description: English: Kiwi with egg in the Kauri Museum, New Zealand Opisthocomus hoazin; Beni River, Bolivia English: Hoatzin, Beni River, Bolivia. English: Male ostrich in Ngorongoro Deutsch: Männlicher Afrikanischer Strauß in Ngorongoro 27/09/1998 Broad-billed Hummingbird male, Madera Canyon, Arizona English: Mute Swan 日本語: コブハクチョウ Eagle Owl English: Flamingo Français&#160;: Flamant rose English: A western gull (larus occidentalis), taken in Santa Barbara, California. Français&#160;: Un Goéland d'Audubon (larus occidentalis). Photo prise à Santa Barbara, en Californie (États-Unis ). Yellow-naped Amazon (Amazona auropalliata) English: Pied Crow (Corvus albus), Etosha National Park, Namibia Deutsch: Schildrabe (Corvus albus), Etosha-Nationalpark, Namibia فارسی: کلاغ سینه‌سفید، در پارک ملی اتوشا Geococcyx californianus English: A Greater Roadrunner in California, USA. Dryocopus pileatus A Pileated Woodpecker 2004-05-29. Photo taken by user Lorax Pélicans des Dombes - France English: Headshot of a Victoria Crowned Pigeon, taken in Jurong Bird Park, Singapore.
context_page_description: The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. Birds are categorized as a biological class, Aves. For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird. Modern phylogenies place birds in the dinosaur clade Theropoda. According to the current consensus, Aves and a sister group, the order Crocodilia, together are the sole living members of an unranked "reptile" clade, the Archosauria. Four distinct lineages of bird survived the Cretaceous–Paleogene extinction event 66 million years ago, giving rise to ostriches and relatives, ducks and relatives, ground-living fowl, and "modern birds".
  Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of a specific modern bird species, and either Archaeopteryx, or some prehistoric species closer to Neornithes. If the latter classification is used then the larger group is termed Avialae. Currently, the relationship between dinosaurs, Archaeopteryx, and modern birds is still under debate.
context_section_description: The phylogenetic classification of birds is a contentious issue. Sibley & Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds (although frequently debated and constantly revised). A preponderance of evidence suggests that most modern bird orders constitute good clades. However, scientists are not in agreement as to the precise relationships between the main clades. Evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem but no strong consensus has emerged.
caption: The diversity of modern birds
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