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''Archaeopteryx'' ( ), sometimes referred to by its German name ''ドイツ語:Urvogel'' ("original bird" or "first bird"), is a genus of bird-like dinosaurs that is transitional between non-avian feathered dinosaurs and modern birds. The name derives from the ancient Greek (''archaīos'') meaning "ancient", and (''ptéryx''), meaning "feather" or "wing". Between the late nineteenth century and the early twenty-first century, ''Archaeopteryx'' had been generally accepted by palaeontologists and popular reference books as the oldest known bird (member of the group Avialae). However, older potential avialans have since been identified, including ''Anchiornis'', ''Xiaotingia'', and ''Aurornis''. ''Archaeopteryx'' lived in the Late Jurassic around 150 million years ago, in what is now southern Germany during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals possibly attaining the size of a raven,〔 the largest species of ''Archaeopteryx'' could grow to about in length. Despite their small size, broad wings, and inferred ability to fly or glide, ''Archaeopteryx'' had more in common with other small Mesozoic dinosaurs than with modern birds. In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes ("killing claw"), feathers (which also suggest warm-bloodedness), and various features of the skeleton.〔〔 These features make ''Archaeopteryx'' a clear candidate for a transitional fossil between non-avian dinosaurs and birds.〔〔 Thus, ''Archaeopteryx'' plays an important role, not only in the study of the origin of birds, but in the study of dinosaurs. It was named from a single feather in 1861.〔 That same year, the first complete specimen of ''Archaeopteryx'' was announced. Over the years, ten more fossils of ''Archaeopteryx'' have surfaced. Despite variation among these fossils, most experts regard all the remains that have been discovered as belonging to a single species, although this is still debated. Most of these eleven fossils include impressions of feathers. Because these feathers are of an advanced form (flight feathers), these fossils are evidence that the evolution of feathers began before the Late Jurassic.〔 The type specimen of ''Archaeopteryx'' was discovered 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. == Description == ''Archaeopteryx'' lived during the early Tithonian stage of the Jurassic period, approximately 150.8–148.5 million years ago. Most of the 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.〔 ''Archaeopteryx'' was roughly the size of a raven,〔 with broad wings that were rounded at the ends and a long tail compared to its body length. It could reach up to in body length, with an estimated mass of .〔 ''Archaeopteryx'' feathers, although less documented than its other features, were very similar in structure and design to modern-day bird feathers.〔 Despite the presence of numerous avian features,〔 however, ''Archaeopteryx'' had many non-avian theropod dinosaur characteristics. Unlike modern birds, ''Archaeopteryx'' had small teeth,〔 as well as a long bony tail, features which ''Archaeopteryx'' shared with other dinosaurs of the time.〔 Because it displays a number of features common to both birds and non-avian dinosaurs, ''Archaeopteryx'' has often been considered a link between them.〔 In the 1970s, John Ostrom, following T. H. Huxley's lead in 1868, argued that birds evolved within 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 along with 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.〔〔〔〔〔〔〔〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Archaeopteryx」の詳細全文を読む スポンサード リンク
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