| Birds are bipedal, warm-blooded,
| |
| | Hesperornithiformes, a group of
|
| oviparous vertebrate animals
| |
| | flightless divers resembling grebes and
|
| characterized primarily by feathers,
| |
| | loons.
|
| forelimbs modified as wings, and (in
| |
| | The recently discovered dromaeosaur
|
| most) hollow bones. All birds reproduce
| |
| | Cryptovolans was capable of powered
|
| sexually, although parthenogenetic eggs
| |
| | flight, possessed a sternal keel and had
|
| are known to be produced by the
| |
| | ribs with uncinate processes. In fact,
|
| domesticated turkey on occasion and
| |
| | Cryptovolans makes a better "bird" than
|
| suspected to occur in its wild ancestor .
| |
| | Archaeopteryx which is missing some of
|
| Birds range in size from the tiny
| |
| | these modern bird features. Because of
|
| hummingbirds to the huge Ostrich and Emu.
| |
| | this, some paleontologists have suggested
|
| Depending on the taxonomic viewpoint,
| |
| | that dromaeosaurs are actually basal
|
| there are about 8,800–10,200 living
| |
| | birds whose larger members are
|
| bird species (and about 120–130 that
| |
| | secondarily flightless, i.e. that
|
| have become extinct in the span of human
| |
| | dromaeosaurs evolved from birds and not
|
| history) in the world, making them the
| |
| | the other way around. Evidence for this
|
| most diverse class of terrestrial
| |
| | theory is currently inconclusive, but
|
| vertebrates.
| |
| | digs continue to unearth fossils
|
| Birds feed on nectar, plants, seeds,
| |
| | (especially in China) of the strange
|
| insects, fish, mammals, carrion, or other
| |
| | feathered dromaeosaurs. At any rate, it
|
| birds.
| |
| | is fairly certain that avian flight
|
| Most birds are diurnal, or active during
| |
| | existed in the mid-Jurassic and was
|
| the day, but some birds, such as the owls
| |
| | "tried out" in several lineages and
|
| and nightjars, are nocturnal or
| |
| | variants by the mid-Cretaceous.
|
| crepuscular (active during twilight
| |
| | Although ornithischian (bird-hipped)
|
| hours), and many coastal waders feed when
| |
| | dinosaurs share the same hip structure as
|
| the tides are appropriate, by day or
| |
| | birds, birds actually originated from the
|
| night.
| |
| | saurischian (lizard-hipped) dinosaurs (if
|
| Many birds migrate long distances to
| |
| | the dinosaurian origin theory is
|
| utilise optimum habitats (e.g., Arctic
| |
| | correct), and thus arrived at their hip
|
| Tern) while others spend almost all their
| |
| | structure condition independently. In
|
| time at sea (e.g. the Wandering
| |
| | fact, the bird-like hip structure also
|
| Albatross). Some, such as Common Swifts,
| |
| | developed a third time among a peculiar
|
| stay aloft for days at a time, even
| |
| | group of theropods, the
|
| sleeping on the wing.
| |
| | Therizinosauridae.
|
| Common characteristics of birds include a
| |
| | An alternate theory to the dinosaurian
|
| bony beak with no teeth, the laying of
| |
| | origin of birds, espoused by a few
|
| hard-shelled eggs, high metabolic rate, a
| |
| | scientists (most notably Lary Martin and
|
| 4-chambered heart, and a light but strong
| |
| | Alan Feduccia), states that birds
|
| skeleton. Most birds are characterised by
| |
| | (including maniraptoran "dinosaurs")
|
| flight, though the ratites are
| |
| | evolved from early archosaurs like
|
| flightless, and several other species,
| |
| | Longisquama, a theory which is contested
|
| particularly on islands, have also lost
| |
| | by most other scientists in paleontology,
|
| this ability. Flightless birds include
| |
| | and by experts in feather development and
|
| the penguins, ostrich, kiwi, and the
| |
| | evolution such as R.O. Prum. See the
|
| extinct Dodo. Flightless species are
| |
| | Longisquama article for more on this
|
| vulnerable to extinction when humans or
| |
| | alternative.
|
| the mammals they introduce arrive in
| |
| | Modern birds are classified in
|
| their habitat. The Great Auk, flightless
| |
| | Neornithes, which are now known to have
|
| rails, and the moa of New Zealand, for
| |
| | evolved into some basic lineages by the
|
| example, all became extinct due to human
| |
| | end of the Cretaceous (see Vegavis). The
|
| influence.
| |
| | Neornithes are split into the
|
| Birds are among the most extensively
| |
| | Paleognathae and Neognathae. The
|
| studied of all animal groups. Hundreds of
| |
| | paleognaths include the tinamous (found
|
| academic journals and thousands of
| |
| | only in Central and South America) and
|
| scientists are devoted to bird research,
| |
| | the ratites. The ratites are large
|
| while amateur enthusiasts (called
| |
| | flightless birds, and include ostriches,
|
| birdwatchers, twitchers or, more
| |
| | cassowaries, kiwis and emus (though some
|
| commonly, birders) probably number in the
| |
| | scientists suspect that the ratites
|
| millions.
| |
| | represent an artificial grouping of birds
|
| There is significant evidence that birds
| |
| | which have independently lost the ability
|
| evolved from theropod dinosaurs,
| |
| | to fly in a number of unrelated
|
| specifically, that birds are members of
| |
| | lineages). The basal divergence from the
|
| Maniraptora, a group of theropods which
| |
| | remaining Neognathes was that of the
|
| includes dromaeosaurs and oviraptorids,
| |
| | Galloanseri, the superorder containing
|
| among others. As more non-avian theropods
| |
| | the Anseriformes (ducks, geese and
|
| that are closely related to birds are
| |
| | swans), and the Galliformes (the
|
| discovered, the formerly clear
| |
| | pheasants, grouse, and their allies). See
|
| distinction between non-birds and birds
| |
| | the chart for more information.
|
| becomes less so. Recent discoveries in
| |
| | The classification of birds is a
|
| northeast China (Liaoning Province),
| |
| | contentious issue. Sibley & Ahlquist's
|
| demonstrating that many small theropod
| |
| | Phylogeny and Classification of Birds
|
| dinosaurs had feathers, contribute to
| |
| | (1990) is a landmark work on the
|
| this ambiguity.
| |
| | classification of birds (although
|
| The basal bird Archaeopteryx, from the
| |
| | frequently debated and constantly
|
| Jurassic, is well-known as one of the
| |
| | revised). A preponderance of evidence
|
| first "missing links" to be found in
| |
| | seems to suggest that the modern bird
|
| support of evolution in the late 19th
| |
| | orders constitute accurate taxa. However,
|
| century, though it is not considered a
| |
| | scientists are not in agreement as to the
|
| direct ancestor of modern birds.
| |
| | relationships between the orders;
|
| Confuciusornis is another early bird; it
| |
| | evidence from modern bird anatomy,
|
| lived in the Early Cretaceous. Both may
| |
| | fossils and DNA have all been brought to
|
| be predated by Protoavis texensis, though
| |
| | bear on the problem but no strong
|
| the fragmentary nature of this fossil
| |
| | consensus has emerged. More recently, new
|
| leaves it open to considerable doubt if
| |
| | fossil and molecular evidence is
|
| this was a bird ancestor. Other Mesozoic
| |
| | providing an increasingly clear picture
|
| birds include the Enantiornithes,
| |
| | of the evolution of modern bird orders.
|
| Yanornis, Ichthyornis, Gansus and the
| |
| | See also: Sibley-Ahlquist taxonomy.
|
