The majority of the plant-eating sauropods died out in most areas by the end of the Jurassic period and beginning of the Cretaceous period. Some scientists believe this was the result of the switch from eating the usual plants to the new angiosperms (flowering plants). The Cretaceous period ornithopods had teeth that were apparently better adapted to chewing the new plants than the sauropods—especially the ornithopods’ multiple rows of teeth inside their jaws. When the teeth in the top row were ground down, new ones shifted to replace the worn ones.