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Archaeopteryx

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Majir
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« on: January 19, 2011, 01:27:51 pm »

Archaeopteryx was a primitive bird that lived during the early Tithonian stage of the Jurassic Period, around 150.8–148.5 million years ago.[7] The only specimens of Archaeopteryx that have been discovered come from the Solnhofen limestone in Bavaria, southern Germany, which is a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils.[8][9]

Archaeopteryx was roughly the size of a raven,[1] with broad wings that were rounded at the ends and a long tail compared to its body length. It could reach up to 500 millimetres (20 in) in body length, with an estimated weight of 0.8 to 1 kilogram (1.8 to 2.2 lb).[1] Archaeopteryx feathers, although less documented than its other features, were very similar in structure and design to modern-day bird feathers.[8] However, despite the presence of numerous avian features,[10] Archaeopteryx had many theropod dinosaur characteristics. Unlike modern birds, Archaeopteryx had small teeth[8] as well as a long bony tail, features which Archaeopteryx shared with other dinosaurs of the time.[11]

Because it displays a number of features common to both birds and dinosaurs, Archaeopteryx has often been considered a link between them—possibly the first bird in its change from a land dweller to a bird.[8] In the 1970s, John Ostrom, following T. H. Huxley's lead in 1868, argued that birds evolved from theropod dinosaurs and Archaeopteryx was a critical piece of evidence for this argument; it had a number of avian features, such as a wishbone, flight feathers, wings and a partially reversed first toe, and a number of dinosaur and theropod features. For instance, it has a long ascending process of the ankle bone, interdental plates, an obturator process of the ischium, and long chevrons in the tail. In particular, Ostrom found that Archaeopteryx was remarkably similar to the theropod family Dromaeosauridae.[12][13][14][15][16][17][18][19][20]

The first remains of Archaeopteryx were discovered in 1861; just two years after Charles Darwin published On the Origin of Species. Archaeopteryx seemed to confirm Darwin's theories and has since become a key piece of evidence for the origin of birds, the transitional fossils debate, and confirmation of evolution. Indeed, further research on dinosaurs from the Gobi Desert and China has since provided more evidence of a link between Archaeopteryx and the dinosaurs, such as the Chinese feathered dinosaurs. Archaeopteryx is close to the ancestry of modern birds, and it shows most of the features one would expect in an ancestral bird. However, it may not be the direct ancestor of living birds, and it is uncertain how much evolutionary divergence was already present among other birds at the time.

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