Today, most animals that eat plants chew their food. Think of a cow: it spends its day chewing its cud, in a grinding fashion. The jaw slides across, grinding plant material between the teeth. The lower jaw is hinged to the skull and the upper jaw.
The hadrosaurs of the dinosaur world might have fit a similar niche to grazers like cows, but how they ate was entirely different. In fact, nothing alive today eats in a way even close to the way the duck-billed dinosaurs did. Hadrosaurs do not have a complex hinging jaw like most mammals of today; instead, their upper jaw was hinged to the rest of the skull. Biting down forced the upper jaws outward, grinding the multiple rows of teeth together and chewing the food. This created complex wear patterns, showing teeth grinding together backwards, forwards, and side to side.
The idea of hadrosaurs chewing in this fashion has been around for 25 years. However, proving this theory was a challenge. The skulls of hadrosaurs are, obviously, fossilized, and so can't be manipulated the same way the skull of a modern animal could be. Direct observation is also impossible. Thus, paleontologists recently turned to the microscopic scratches on hadrosaur teeth. These scratches are distinctive enough to tell the researchers exactly how the dinosaurs chewed. It even revealed what they ate. Hadrosaurs might have been either grazers, chipping plants close to the ground, or browsers, pulling leaves and branches off of trees and bushes. The scratches reveal that hard particles, perhaps dirt or silica, were chewed on as well as the plant material. This is distinctive of grazers, as dirt often gets mixed in with the ground vegetation and silica is found in grasses and other grazed plants.
So, from the tiny scratches on a single tooth, paleontologists have solved the mysteries of what and how the hadrosaurs ate. It's remarkable how much we can learn about these fantastic animals from such a small part as a tooth.
Credit: Science Daily, "Dino Tooth Sheds New Light On Ancient Riddle"