Bird-archosaurs (the Ornithosuchia) have played major roles in terrestrial ecosystems for over 200 million years, and they continue to do so in the form of 9,000 living species of birds. But very little is known of the early evolution of bird- archosaurs. This grant will enable a more comprehensive investigation of this problem than has yet been possible. Clearer understanding of genealogical relationships among the early ornithosuchians will serve as a basis for evaluating major aspects of their evolutionary history.