BIRD on fossil and biological evidence, most scientists accept that birds are a specialized subgroup of theropod dinosaurs.[14] More specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others.[15] As scientists have discovered more nonavian theropods closely related to birds, the previously clear distinction between nonbirds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod dinosaurs had feathers, contribute to this ambiguity.[16] Nonetheless, on 31 July 2014, scientists reported details of the evolution of birds from theropod dinosaurs.[3][4]
The consensus view in contemporary paleontology is that the birds, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids.[17] Together, these form a group called Paraves. Some basal members of this group, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both.[18][19] Unlike Archaeopteryx and the non-avian feathered dinosaurs, who primarily ate meat, recent studies suggest that the first birds were herbivores.[20]
Confuciusornis sanctus, a Cretaceous bird from China
The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, as well as wings with flight feathers identical to those of modern birds. It is not considered a direct ancestor of modern birds, though it is possibly closely related to the real ancestor.[21]
During their evolution from eumaniraptoran ancestors to modern forms, birds have shown increasing tendencies towards progenesis, where they become sexually mature at an earlier stage in their development, most noticeable in the Passerines.[22][23]
The consensus view in contemporary paleontology is that the birds, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids.[17] Together, these form a group called Paraves. Some basal members of this group, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both.[18][19] Unlike Archaeopteryx and the non-avian feathered dinosaurs, who primarily ate meat, recent studies suggest that the first birds were herbivores.[20]
Confuciusornis sanctus, a Cretaceous bird from China
The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, as well as wings with flight feathers identical to those of modern birds. It is not considered a direct ancestor of modern birds, though it is possibly closely related to the real ancestor.[21]
During their evolution from eumaniraptoran ancestors to modern forms, birds have shown increasing tendencies towards progenesis, where they become sexually mature at an earlier stage in their development, most noticeable in the Passerines.[22][23]
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