T. rex and Triceratops are among the best-studied dinosaurs of all time. How much more can we learn? Surprisingly, more than we ever thought. Famed paleontologist Jack Horner and his colleagues are challenging the long held belief that young dinosaurs looked like miniature versions of their parents. Instead they may have looked so different that scientists assumed juveniles and adults were separate species. Even a young T. rex it would be hard to recognize. The transformations from childhood to adulthood were so dramatic that Horner suspects that up to a third of all dinosaur species may vanish in cases of mistaken identity. In their place were developing a new understanding of the complexity of dinosaur lives and learning new reasons for some of the dinosaurs' strangest features like horns lumps, bumps, and dome-heads.