Bird

Many - see section below.

Evolution

Birds are generally considered to have evolved from theropod dinosaurs. Specifically, birds are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids. As more non-avian theropods that are closely related to birds are discovered, the formerly clear distinction between non-birds and birds becomes less so. Recent discoveries in North-east China (Liaoning Province) demonstrating that many small theropod dinosaurs had feathers contribute to this ambiguity.

Related Topics:
Theropod - Dinosaur - Maniraptora - Dromaeosaur - China - Liaoning - Feather

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The basal bird Archaeopteryx, from the Jurassic, is well-known as one of the first "missing links" to be found in support of evolution in the late 19th century. It remains the most primitive known bird. Other Mesozoic birds include the Confuciusornithidae, Enantiornithes, Ichthyornis, and Hesperornithiformes, a group of flightless divers resembling grebes and loons.

Related Topics:
Archaeopteryx - Jurassic - Evolution - 19th century - Mesozoic - Confuciusornithidae - Enantiornithes - Ichthyornis - Hesperornithiformes - Grebe - Loon

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The recently discovered dromaeosaur, Cryptovolans, was capable of powered flight, contained a keel and had ribs with uncinate processes. In fact, Cryptovolans makes a better "bird" than Archaeopteryx which is missing some of these modern bird features. Because of this, some paleontologists have suggested that dromaeosaurs are actually basal birds whose larger members are secondarily flightless, i.e. dromaeosaurs evolved from birds and not the other way around. Evidence for this theory is currently inconclusive, but digs continue to unearth fossils (especially in China) of the strange feathered dromaeosaurs.

Related Topics:
Cryptovolans - Keel - Uncinate - Archaeopteryx - Dromaeosaur

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It should be noted that although ornithischian (bird-hipped) dinosaurs share the same hip structure as birds, birds actually originated from the saurischian (lizard-hipped) dinosaurs, and thus arrived at their hip structure condition independently. In fact, the bird-like hip structure developed a third time among a peculiar group of theropods, the Therizinosauridae.

Related Topics:
Ornithischia - Hip - Saurischia - Independently - Therizinosauridae

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Modern birds are classified in Neornithes, which are split into the Paleognathae and Neognathae. The paleognaths include the tinamous (found only in Central and South America) and the ratites. The ratites are large flightless birds, and include ostriches, cassowaries, kiwis and emus; some scientists suspect that the ratites represent an artificial grouping of birds which have independently lost the ability to fly, others contend that the ratites never had the ability to fly and are more directly related to the dinosaurs. The basal divergence from the remaining Neognathes was that of the Galloanseri, the superorder containing the Anseriformes (ducks, geese and swans), and the Galliformes (the pheasants, grouse, and their allies). See the chart.

Related Topics:
Tinamou - Ratite - Anseriformes - Duck - Geese - Swan - Galliformes - Pheasant - Grouse

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The 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). Evidence for the various orders seems to be fairly good, but the relationships between the orders are in a state of disarray. Evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem but no strong consensus has emerged. See also: Sibley-Ahlquist taxonomy.

Related Topics:
Sibley - Sibley-Ahlquist taxonomy

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