Modern vertebrates have highly modular skulls composed of multiple bone elements separated by and integrated together by sutures. Such modularity allows for independent growth of individual skull bones. Sutures are a critical component of modular skulls and important to their normal morphology, organization, composition and function. However, evolution of developmental mechanisms regulating suture formation is poorly understood. We propose to use computer tomography and high-power synchrotron scans to analyze important fossils and broadly survey extant vertebrate taxa to document the diversification of sutural morphologies. These descriptive studies will help us trace evolutionary history of the skull sutures. Next, we will investigate developmental and molecular mechanisms that regulate changes in initiation, maintenance and fusion of sutures in the skulls of chicken embryos, a well-established laboratory model. Uncovering such mechanisms during both normal and abnormal development will allow us to test specific hypotheses related to the role of sutures in the skull evolution as well as cranial abnormalities in humans. Lastly, we will address how changes in regulation of suture development can explain major evolutionary transitions in the reptilian and avian skulls, e.g. dramatic fusion and/or loss of bones in birds as compared with their dinosaurian ancestors and crocodilian relatives. PhD student on this project will be trained in morphometric analyses and experimental cell and developmental biology techniques, including manipulation of chicken and mouse embryos in vivo and using advanced 3D skeletogenic tissue culture (developed in collaboration with Dr. Demirci, Stanford University) to address major questions of skull evolution and development.