All of today’s Reptilia are cheekless. Their open mouth-line extends all the way back to the joint of the jaw before the ears. There is no skin to hold any food being chewed. Consequently, herbivorous reptiles—tortoises and iguana lizards, for example— are sloppy eaters; (real size animatronic dinosaur)when their jaws slice off a piece of leaf, the part sticking out of the mouth simply falls to the ground. Each time they chew, they lose nearly half their mouthful, quite a wasteful business. Primitive meat-eating dinosaurs had similar wide open mouth lines.
Traditionally, duckbill dinosaurs have been portrayed as cheekless, with the mouth line running from chin to ear like a lizard’s.(lifelike dinosaur model) A dissenting voice was raised by Yale Professor Richard Swann Lull (Yale’s tradition of duckbills seems to have been consistently heterodox). In 1942, Lull restored duckbills with cow-style cheeks walling the sides of the oral space. (zigong dinosaur factory)But most of Lull’s colleagues rejected the idea because everyone knew dinosaurs were reptiles, and reptiles, by definition, didn’t have cheeks. Such objections were specious. No living reptile has cheeks. But no living reptile has grinding teeth anything remotely resembling those of a duckbill. If the duckbills could have evolved such unreptilian teeth, why couldn’t they have evolved unreptilian cheeks?