Duckbilled dinosaurs—hadrosaurs, the most common plant-eaters of their time—chewed their food differently from any animal alive today.

Using an electron scanning microscope, researchers were able to examine minute scratches on individual dino teeth made by daily wear and tear 65 million to 68 million years ago to test competing theories about how the creatures may have munched.

Unlike most animals, which have a complex joint on the lower jaw, these dinosaurs had a hinge between the upper jaw and the rest of the skull to allow for much more movement than many of their peers had. The tiny scratches show that when they chomped down on food—likely cattails and other low vegetation—the upper jaw would be forced outward, sliding teeth sideways across those in the lower jaw. This motion, combined with up, down, front and back movements, would shred and grind fibrous plant material that made up their diets.

The findings appear in the latest Proceedings of the National Academy of Sciences. Before the analysis, some doubted that this imaging technique could be fruitfully used on dinosaur teeth, which were replaced frequently throughout the animal’s life.

“By looking at the pattern of scratches in an area that is only about as wide as a couple human hairs we can work out how and what these huge herbivores were eating,” lead study author from the University of Leicester, Vince Williams, said in a statement. “Because we can analyze single teeth…the technique has the potential to tell us a lot more about dinosaur feeding and the ecosystems in which they lived.”

Image of teeth from the lower jaw of an Edmontosaurus, courtesy of Vince Williams, University of Leicester