Hadrosaurid (duckbilled) dinosaurs are well-known for their pronounced beaks, and Shantungosaurus stands out even in such an orally impressive family. It was a hadrosaurine (non-crested duckbill), a subfamily of duckbills which had wider beaks than did their crested cousins, the lambeosaurines. In addition, it was a huge hadrosaur, rivalling in length and mass many of the smaller sauropods while maintaining the massive masticatory mechanisms of wide-snouted duckbills. But beyond family and size, Shantungosaurus took its mandibular predisposition to another level, modifying the typically long, low, tapering duckbill jaw into a tall, blocky jaw that is almost rectangular in profile.

The bill, however, is only the front of the amazing hadrosaurid mouth. Further back, the jaws were lined with thousands of closely packed teeth, forming a rasp-like dental battery capable of pulping the toughest foliage. And duckbills put their teeth to good use - hadrosaurids and other advanced ornithopods did something unique in reptilian evolution - they developed a way to chew.

Mammals chew by rotating the lower jaw against the upper one - even our modest ability to wiggle our chin is a skeletal impossiblility in reptiles, whose lower jaws move in a simple up/down plane. However, the bones of the skull, and especially the jaws, are not rigidly fused in most reptiles. Duckbills were able to side the grinding surfaces of their teeth across each other by flexing their upper jaws outwardly.

Imagine the only teeth in your head were your molars - all your front teeth and lips were replaced by a horny beak. Now picture your lower jaw capable of only the simplest up-and-down motions. Yet your molar-bearing upper jawbones (the maxillae) are flexible. You bite off a chunk of food with your beak, and your tongue pulls it back into your mouth. As you close your jaw, your lower molars push up against your upper teeth, causing the maxillae to spread outward, which slides the upper teeth across the lower ones. In effect, you are chewing sideways, with the food on each side of your mouth being chewed in opposite directions.