To answer this question, there are several ways. Some of the dinosaurs become fossils preserved stomach contents, these straightforward tell us of their Last Supper. Some are considered the fossil dinosaur dung, told us the dinosaurs food is difficult to digest things. but the evidence is not only extremely rare, and were considered to be dinosaurs found in the stool is not necessarily a dinosaur. carnivorous dinosaur tooth shape, the prey with the teeth marks left on bones by comparing and the evidence in the fossil record is very common, but also provides a more reliable evidence. But this method can not be used in food plant dinosaur body. One way is to study the eating dinosaur's teeth planted a tiny structure (tooth surface scratches and small points). Quantitative study of the micro-structure of the teeth can be distinguished dinosaurs were grazing or eating leaves. Those grazing the surface of the animal's teeth, not many small point, but with a large number of scratches; while those who ate the animal leaves the surface of teeth, there are many pits (which is caused due to hard trees), and scratches. The teeth of mammals have been very broad, and mammal teeth can be identified on the scratch they eat specific plants. As the geological history of the evolution of different plant produces a variety of ways to resist the fresh plant animals. Them through changes in their chemical composition and in the leaves and stems to add more fiber, make them harder to digest and chew animals. Some of the stems of plants added to the composition of opal phytolith, to make them harder to chew the stems, so the different plants in the animal's teeth, left a different mark. On the micro-structure of human teeth studies have found that different foods (such as wheat and barley), in the teeth on the left a different micro-structures. In the Early Cretaceous angiosperm radiation, leading to great changes in the plant kingdom, but also correspond to ornithopod specialization. We (the British scholar and his Chinese female students) Application mammals mature Dental Research methods, ornithopod micro-structure of the teeth were studied to understand the Early Cretaceous earth-shattering changes, which have taken place in how the Food and change. We (the British scholar and his Chinese female students) also studied the application of this approach dinosaur chewing way. Scratch the direction of dinosaur teeth told us of their activities in the direction of the mouth, while the extent of tooth scratches parallel to tell us the way with a specific chewing. Scratch in a specific direction of the frequency allows us to distinguish different ways to chew some different directions. The previous method of combining these methods, you can help us understand the direction and intensity of the dinosaurs chewing tension. Preliminary studies have shown that chewing ornithopod way than we previously thought is far more complex.