Many of the plant eating dinosaurs had a horny beak with which they cropped the vegetation that they ate. Unlike modern grazing animals, which use their lips to grasp food and pull it into their mouth, reptiles have no lips. The dinosaurs had to cut and tear their food with their beak, before grinding it up with rows of teeth at the back of their mouth.
True beaked dinosaurs evolved at about the same time as the appearance of the first modern flowering plants, so the parrot-like beak may have been an adaptation that allowed them to take advantage of this new food source.
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