Our studies of bird evolution — the late evolution of dinosaurs — include a comprehensive program on the diversity and genealogical relationships of Mesozoic birds and their modern relatives. In the last few decades, the number of species of early birds has more than tripled those known for the previous century. Our work has been at the center of these discoveries. A host of different primitive lineages of birds that lived alongside large dinosaurs have been studied and numerous new species have been named. In collaboration with a number of other researchers, we have also conducted research on the evolutionary relationships, growth, and development, and life histories of early birds. This work has filled a significant gap in our knowledge of the Mesozoic evolution of birds. Our work has also been extended to understand better the early evolutionary divergences of modern birds.