For the angled wear surfaces to have developed, there would have had to be some ability of the jaws to move sideways as they closed. Animatronic dinosaur costume This type of movement is achieved in living herbivorous mammals through the development of an anisognathic jaw closure mechanism. This relies on the fact that the lower jaws are naturally narrower than the upper jaws. Special muscles, arranged in a sling on either side of each jaw bone, are capable to controlling the position of the jaw very precisely so that the teeth on one side meet one another and then the lower set is forcibly slid inwards so that the teeth grind against one another. Realistic dinosaur costume We humans employ this type of jaw mechanism, especially when eating tough foods, but it is far more exaggerated in some classically herbivorous mammals such as cows, sheep, and goats, where the swing of the jaw is very obvious.
The whole mammalian type of jaw mechanism is dependent upon very complex jaw muscles, a complex nervous control system, and a specially constructed set of skull bones to withstand the stresses associated with this chewing method. By contrast, more conventional reptiles of which Iguanodon was one, do not have an anisognathic jaw arrangement, lack the complex muscular arrangements that allow the lower jaw to be very precisely positioned (whether they had the nervous system to control such movements is largely irrelevant), and their skulls are not specially reinforced to withstand the lateral forces acting on the skull bones.