Duckbill dinosaurs had plant-pulverizing teeth more advanced than even cows, horses and other well-known modern grazers, U.S. paleontologists say.

In the first study to ever recover material properties from fossilized teeth, scientists examined the jaws of duckbill dinosaurs, also known as hadrosaurids, which were the dominant plant-eaters in the Late Cretaceous about 85 million years ago, the American Museum of Natural History reported.

They discovered hadrosaurids actually had six types of dental tissues -- four more than reptiles and two more than modern expert mammal grinders such as horses, cows and elephants.

"We were stunned to find that the mechanical properties of the teeth were preserved after 70 million years of fossilization," said lead author Gregory Erickson, a biology professor at Florida State University, who described hadrosaurids as "walking pulp mills."

Their broad jaws bearing as many as 1,400 teeth suggest hadrosaurids evolved the most advanced grinding capacity known in vertebrate animals, the researchers said.

"Their complex dentition could have played a major role in keeping them on the planet for nearly 35 million years," American Museum of Natural History paleontologist Mark Norell said.