By the end of the 1980s, most palaeontologists accepted that birds were the descendants of bipedal, mainly carnivorous dinosaurs known as theropods. At that time, the only known fossil to document the evolutionary transition to birds was Archaeopteryx from the Jurassic Period which was discovered in Germany.
This changed with the discovery in the mid-1990s of the Jehol Biota, an assemblage of Early Cretaceous fossils from northeast China. An assemblage is a group of fossils found together in a defined region. Fossils found in the Jehol Biota included primitive birds and closely related non-avian theropods. Similar specimens were also found in the Yanliao Biota, an assemblage of Jurrasic Period fossils from the same area of China.
The Jehol and Yanliao Biotas are characterized by exceptional fossil preservation, with skeletons accompanied by feathers and other soft tissues. Specimens from the Jehol Biota show that non-avian theropods had feathers similar in structure to those of modern birds. Many other specimens had feathers that indicated they originally evolved for display or insulation, rather than flight.
In this presentation, Dr. Corwin Sullivan, University of Alberta, discusses the Jehol and Yanliao Biotas, and the wide diversity of anatomical structures potentially related to flight in early birds and their close relatives.