hadrosaur chewing

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From Wikipedia:

The study found that the hadrosaur chewed using a method completely different than any creature living today,^[7] and utilized a type of jaw that is now extinct.^[8] The study found the Edmontosaurus jaw had four different sets of parallel scratches running in different directions. Purnell concluded each set of scratches related to a specific jaw movement. This revealed the movement of hadrosaurs was complex and employed movement in several different directions, including up-and-down, front-to-back and sideways movements. The trio concluded that in contrast to the flexible lower jaw joint prevalent in modern mammals, the hadrosaur had a hinge between its upper jaws and the rest of its skull.^[7] According to the study, the hadrosaur would push its upper jaws outwards and sideways, while the lower teeth slid against the upper teeth.^[29] As the tooth surfaces slid sideways across each other, the food would be ground and shredded before consumption.^[8] Purnell said the style of eating, "was not a scissor-like movement; it seems that these dinosaurs invented their own way of chewing."^[29] Although the upper-jaw teeth hinged outward when the hadrosaur ate, Purnell said it was likely the dinosaur could still chew with its mouth closed. While the outward flexure of the upper jaws might have been visible, Purnell said the chewing was likely concealed by the hadrosaur's cheeks and probably looked "quite subtle".^[31]


At least as interesting as the fact that they had a unique way of chewing, I think, is how we know that:

The specific Edmontosaurus jaw used in this study was collected from Late Cretaceous rocks found in the United States.^[28][29] The individual teeth on the jaw contained multiple hundreds of microscopic scratches, which had been preserved intact during fossilization. The researchers carefully cleaned the jaws, molded them and coated them with gold to make a detailed replica of the tooth surface. Then they used a scanning electron microscope to give high-power magnification of the scratches for study, and conducted a three-dimensional statistical analysis of the direction of the scratches.^[8][28][29]


And:

The scratches found on each individual tooth were so equal that measuring an area of just one square millimeter was enough to sample the whole jaw. The team concluded the evenness of the scratches suggested the hadrosaur used the same series of jaw motions over and over again. As a result, the study determined that the hadrosaur diet was probably made of leaves and lacked the bulkier items such as twigs or stems, which might have required a different chewing method and created different wear patterns.^[31]

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