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Paraves is a branch-based clade defined to include all dinosaurs which are more closely related to birds than to oviraptorosaurs. Paravians comprises two major sub-groups: Avialae, including ''Jeholornis'' and modern birds, and the Deinonychosauria, which includes the dromaeosaurids and troodontids, which may or may not form a natural group. == Description == Like other theropods, early paravians were bipedal, walking on their two hind legs. However, whereas most theropods walked with three toes contacting the ground, fossilized footprint tracks confirm that many basal paravians, including dromaeosaurids, troodontids, and some early avialans, held the second toe off the ground in a hyperextended position, with only the third and fourth toes bearing the weight of the animal. This is called functional didactyly. The enlarged second toe bore an unusually large, curved sickle-shaped claw (held off the ground or 'retracted' when walking). This claw was especially large and flattened from side to side in the large-bodied predatory eudromaeosaurs. In these early species, the first toe (hallux) was usually small and angled inward toward the center of the body, but only became fully reversed in more specialized members of the bird lineage.〔 One species, ''Balaur bondoc'', possessed a first toe which was highly modified in parallel with the second. Both the first and second toes on each foot of ''B. bondoc'' were held retracted and bore enlarged, sickle-shaped claws.〔 (Supporting Information )〕 An increasingly asymmetric carpal joint, a trend that can be traced back to primitive coelurosaurs, allowed the forelimbs to elongate and an elaboration of their plumage, traits that made the evolution of wings possible.〔(The asymmetry of the carpal joint and the evolution of wing folding in maniraptoran theropod dinosaurs )〕 The teeth of basal paravians were curved and serrated, but not blade-like except in some specialized species such as ''Dromaeosaurus albertensis''. The serrations on the front edge of dromaeosaurid and troodontid teeth were very small and fine, while the back edge had serrations which were very large and hooked.〔 Paravians generally have long, winged forelimbs, though these have become smaller in flightless birds and some extinct lineages such as the troodontids. The wings usually bore three large, flexible, clawed fingers in early forms.〔 The fingers became fused and stiffened and the claws highly reduced or lost in some advanced lineages. Most dromaeosaurids seem to have been predatory, though some smaller species (especially among the troodontids and avialans) are known to have been at least omnivorous; and it is possible that an omnivorous diet was the ancestral state for this group, with more strict carnivory evolving in some lineages.〔 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「Paraves」の詳細全文を読む スポンサード リンク
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