page_title: Origin of birds
section_title: Feathers
hierarchical_section_title: Origin of birds / Features linking birds and dinosaurs / Feathers
caption_attribution_description: English: Cast of the fossil dromaeosaur specimen NGMC 91 (nicknamed "Dave", cf. Sinornithosaurus), at the American Museum of Natural History in New York.
context_page_description: The scientific question of within which larger group of animals birds evolved has traditionally been called the 'origin of birds'. The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated during the Mesozoic Era.
  A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany. Birds and extinct non-avian dinosaurs share many unique skeletal traits. Moreover, fossils of more than thirty species of non-avian dinosaur with preserved feathers have been collected. There are even very small dinosaurs, such as Microraptor and Anchiornis, which have long, vaned arm and leg feathers forming wings. The Jurassic basal avialan Pedopenna also shows these long foot feathers. Paleontologist Lawrence Witmer concluded in 2009 that this evidence is sufficient to demonstrate that avian evolution went through a four-winged stage. Fossil evidence also demonstrates that birds and dinosaurs shared features such as hollow, pneumatized bones, gastroliths in the digestive system, nest-building and brooding behaviors.
context_section_description: Archaeopteryx, the first good example of a "feathered dinosaur", was discovered in 1861. The first specimen was found in the Solnhofen limestone in southern Germany, which is a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils. Archaeopteryx is a transitional fossil, with features clearly intermediate between those of non-avian theropod dinosaurs and birds. Discovered just two years after Darwin's seminal Origin of Species, its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for Compsognathus.
  Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. The first of these were initially described as simple filamentous protofeathers, which were reported in dinosaur lineages as primitive as compsognathids and tyrannosauroids. However, feathers indistinguishable from those of modern birds were soon after found in non-avialan dinosaurs as well.
  A small minority of researchers have claimed that the simple filamentous "protofeather" structures are simply the result of the decomposition of collagen fiber under the dinosaurs' skin or in fins along their backs, and that species with unquestionable feathers, such as oviraptorosaurs and dromaeosaurs are not dinosaurs, but true birds unrelated to dinosaurs. However, a majority of studies have concluded that feathered dinosaurs are in fact dinosaurs, and that the simpler filaments of unquestionable theropods represent simple feathers. Some researchers have demonstrated the presence of color-bearing melanin in the structures—which would be expected in feathers but not collagen fibers. Others have demonstrated, using studies of modern bird decomposition, that even advanced feathers appear filamentous when subjected to the crushing forces experienced during fossilization, and that the supposed "protofeathers" may have been more complex than previously thought. Detailed examination of the "protofeathers" of Sinosauropteryx prima showed that individual feathers consisted of a central quill (rachis) with thinner barbs branching off from it, similar to but more primitive in structure than modern bird feathers.
caption: Fossil cast of NGMC 91, a probable specimen of Sinornithosaurus
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