As ceratopsids got bigger over time—morphing into bovine versions of dinosaurs that were very common in North America during the latest Cretaceous—they changed their jaws so that they could engulf unholy quantities of plants. They packed their teeth closely together so that the jaws were essentially blades—four in all, one on each side of the upper jaw and one on each side of the lower. The jaws would snap shut in a simple up-and-down motion, the opposing blades slicing past each other like a guillotine. At the front of the snout was a razor-sharp beak, which would pluck the stems and leaves
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