Duck-billed dinosaurs had amazingly complex teeth - much more so than those of cows, horses, and other modern grazers - allowing them to chew tough and abrasive plants with great efficiency.
Also known as hadrosaurids, duck-billed dinosaurs were the dominant plant-eaters in what are now Europe, North America, and Asia during the Late Cretaceous about 85 million years ago.
With broad jaws bearing as many as 1,400 teeth, they were previously thought to have chewing surfaces similar to other reptiles, composed of just two tissues - enamel, a hard hypermineralized material, and orthodentine, a soft bonelike tissue.
But, suspecting there was a bit more going on, a team of scientists and engineers sectioned the fossilized teeth and made microscope slides from them. These revealed that hadrosaurids actually had six different types of dental tissues - four more than reptiles and two more than expert mammal grinders like horses, cows, and elephants.
"We were stunned to find that the mechanical properties of the teeth were preserved after 70 million years of fossilization," says Gregory Erickson, a biology professor at Florida State University. "If you put these teeth back into a living dinosaur, they would function perfectly."
As well as the four dental tissues found in mammals - enamel, orthodentine, secondary dentine and coronal cementum - the hadrosaurid teeth include giant tubules and a thick mantle dentine, thought to provide additional prevention against abscesses.
It now appears that hadrosaurids evolved the most advanced grinding capacity ever known in vertebrate animals, which might have led to their extensive diversification.
"Their complex dentition could have played a major role in keeping them on the planet for nearly 35 million years," says Mark Norell, chair of the American Museum of Natural History.