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Some dentistry work on a 70-million-year-old tooth has provided an insight into the evolutionary success of duck-billed dinosaurs.

Hadrosaurs' unique tooth structure is now a vital clue in the mystery of how the billed herbivores, dubbed "the cows of the Cretaceous era", spread so far and lived for so long. The ancient monsters survived until the very end of the dinosaur age, roughly 65 million years ago.

Biologist Gregory Erickson, of Florida State University in Tallahassee, led a team of scientists who rubbed diamonds on the ancient tooth, provided by the American Museum of Natural History, to simulate the processes of chewing. The fossil was examined with light and electron microscopes to work out the rate at which the tooth was worn down.

The results, published today in the journal Science show how tough the prehistoric grinders were - and they were perfect for grinding and slicing plants that fed the hadrosaurs for so long.

"These guys were like walking pulp mills," Erickson says. Wear on the tooth actually improved its grinding ability, making these toothy dinos dental unparalleled marvels compared to today's chewers - such as horses and buffalos - which have much simpler tooth setups.

Earlier research had shown that hadrosaurs had up to 1,400 teeth packed behind their bills, and that these fell out and were replaced continually over the year, almost like today's sharks that can replace lost teeth with backup pearly whites.

The flat-topped teeth allowed hadrosaurs to grind through low-lying grasses, the tough leaves of plants, such as horsetails and ferns, and the woody bits of conifers.

While most mammals have two types of tissue in their teeth - external enamel and softer dentine inside - and today's humans have four thanks to a second layer of dentine and cementum, these duckbilled dinos had six types of tissue.

The hadrosaur tooth is one of the most sophisticated known to science. ®

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