Feathered dinosaur

Although growing evidence of the relationship of non-avian dinosaurs to birds raised the possibility of feathered dinosaurs over the twentieth century, it was not until the mid-1990s that non-avian dinosaur fossils were discovered with clearly preserved feathers. Since then, feathers or feather-like integument have been discovered on dozens of genera of dinosaurs via both direct and indirect fossil evidence.

Although the vast majority of feather discoveries have been for coeleurosaurian theropods, the discoveries of integument on at least three ornithschians raise the likelihood that proto-feathers were present in basal dinosaurs, and perhaps even a more ancestral animal, in light of the pycnofibers of pterosaurs. Crocodilians also possess beta keratin very similar to those of birds, which suggests that they evolved from a common ancestral gene.

All modern birds possess feathers, with the exception of a few artificially selected chickens.

History of research

Early

Shortly after the 1859 publication of Charles Darwin's On the Origin of Species, British biologist Thomas Henry Huxley proposed that birds were descendants of dinosaurs. He compared the skeletal structure of Compsognathus, a small theropod dinosaur, and the 'first bird' Archaeopteryx lithographica (both of which were found in the Upper Jurassic Bavarian limestone of Solnhofen). He showed that, apart from its hands and feathers, Archaeopteryx was quite similar to Compsognathus. Thus Archaeopteryx represents a transitional fossil. In 1868 he published On the Animals which are most nearly intermediate between Birds and Reptiles, making the case. The leading dinosaur expert of the time, Richard Owen, disagreed, claiming Archaeopteryx as the first bird outside dinosaur lineage. For the next century, claims that birds were dinosaur descendants faded, with more popular bird-ancestry hypotheses including 'crocodylomorph' and 'thecodont' ancestors, rather than dinosaurs or other archosaurs.