Ornithischians (bird-hipped) dinosaurs were divided into two groups:
The earliest Ornithischians include the poorly known Pisanosaurus form South America, and genera such as Heterodontosaurus and Scutellosaurus.
Unlike the Saurichians, they had no teeth in the front of their jaws. Instead, there was a bony structure. In sone ornithischians, this structure developed into a beak very much like that of a bird. The beak was very useful in cutting through tough leaves and woody stems that formed the animal's diet. It also connected the two halves of the lower jaws and enabled them to transmit and absorb force during chewing. the ornithischians evolved later than the saurichians.|