The Early Evolutionary History of Birds

With more than 10,000 species—roughly twice as many as there are mammals or lizards—birds are by far the most diverse group of living land vertebrates. However, this enormous diversity is just a remnant of an ancient evolutionary radiation that can be traced back to the Jurassic, to the 150 million-year-old Archaeopteryx from southern Germany. Research on the early history of birds and the development of flight has been at the forefront of paleontology since the advent of evolutionary thought. For most of this time, however, the available evidence was limited to a small number of fossils largely restricted to near-shore and marine environments, and greatly separated both anatomically and in time. A burst of discoveries of Cretaceous birds over the last two decades has revealed a hitherto unexpected diversity; since the early 1990s, the number of new species described has more than tripled those known for much of the last two centuries. This rapid increase in discoveries has not only filled much of the anatomical and temporal gaps that existed previously, but has also made the study of early birds one of the most dynamic fields of vertebrate paleontology.