‘Existing fossils of four-legged animals, both reptilian and mammalian ancestors, have the same number of upper jaw bones. It's very easy to think that the bones are the same, but now we can study embryos and track cellular development to study these bones in much greater detail,’ explained postdoctoral researcher Hiroki Higashiyama, who studies evolutionary development at the University of Tokyo Graduate School of Medicine. The research, recently published in Proceedings of the National Academy of Sciences, is the first to examine the evolution of facial structure using cellular studies comparing multiple embryos of multiple species.