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Zhenyuanlong
''Zhenyuanlong'' (meaning ''"Zhenyuan's dragon"'', from Chinese Pinyin 龙 lóng ''"dragon"'') is a genus of dromaeosaurid dinosaur from the Yixian Formation of Liaoning, China. It lived during the Aptian age of the early Cretaceous period, approximately 125 million years ago. It is known from a single specimen belonging to the species ''Zhenyuanlong suni''. This type specimen preserved a nearly complete skeleton that contains traces of feathers, including long tail feathers and large wings. In addition to further complicating diversity of Liaoning dromaeosaurids, this specimen provides the first evidence of well-developed pennaceous feathers in a large, non-flying dromaeosaur, raising the question of what function such wings would serve.
==Description==
''Zhenyuanlong suni'' was a mid-sized dromaeosaurid comparable in length to the similar ''Tianyuraptor''. The fossil skeleton is nearly complete but lacks the last half of the tail, giving the specimen a preserved length of . Based on comparison to the complete skeleton of ''Tianyuraptor'', it has been estimated that the skeleton of ''Zhenyuanlong'' would have been about long when complete. With the added length of long tail feathers, the animal was perhaps up to in life.〔 The fossil represents a subadult individual, as shown by the fusion of the neural arches having been progressed into the sacrum.〔
Its overall proportions are comparable to ''Tianyuraptor'', a dromaeosaurid from the same formation, and it bears many anatomical similarities to the other Liaoning dromaeosaurids. The skull is well-preserved and similar in shape to that of ''Tianyuraptor'' and the related ''Sinornithosaurus''. Its sacrum consists of six vertebrae, four of which are clearly fused, and its tail includes the network of bony support rods typical of dromaeosaurs, as well as middle caudal (tail) vertebrae that are somewhat elongated compared to most other dromaeosaurs. Both pectoral girdles are preserved and the specimen shows non-fused sternal plates. Its leg proportions are similar to other Liaoning dromaeosaurs, with its tibiotarsus longer than the femur at a ratio of around 1.30. This large ratio is typical of Liaoning dromaeosaurs but differs from most other dinosaurs in this group.〔
''Zhenyuanlong'' had very short arms and the shortest arm-to-leg length ratio of any known dromaeosaurid except for the basal dromaeosaurid ''Mahakala'' and the giant unenlagiine ''Austroraptor''. Its arms also exhibit some unique and unusual features seen in few related dinosaurs. The radius of ''Zhenyuanlongs forearm is among the proportionally thinnest of any theropod dinosaur, comparable only to a handful of basal coelurosaurs and to alvarezsauroids, which had extremely reduced arms and hands. ''Zhenyuanlong'' is also unique among Liaoning dromaeosaurids for its second metacarpal being shorter than the combined lengths of the first metacarpal and first bone of the innermost finger.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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