This rendering of Gryposaurus monumentensis shows the robust jaws that allowed this creature to eat just about any vegetation it stumbled across.

Credit: Larry Felder

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CHICAGO: Fossil hunters have discovered a new species of duck-billed hadrosaur with an unusual toothy snout in a dinosaur graveyard.

A full-grown adult of Gryposaurus monumentensis could have reached nine metres in length, making it one of the largest hadrosaurs that ever walked the Earth.

"It was one of the most robust duck-billed dinosaurs ever," said Terry Gates, a palaeontologist at the University of Utah's Museum of Natural History in Salt Lake City, USA. "It was a monster."

Hundreds of teeth

The herbivore roamed the planet about 75 million years ago during the late Cretaceous Period, and was almost certainly the master of its domain, towering over the other dinosaurs that populated that part of the western USA.

The creature had a powerful, beak-shaped jaw with 300 teeth capable of slicing through almost any vegetation, and up to 500 replacement choppers embedded in its mammoth jawbone – the lower part of which measured about 70 cm in length.

Fossil hunting volunteers from a Californian museum first discovered the remains of the dinosaur's skull in a remote spot of southern Utah in 2002.

In 2005, palaeontologists from the University of Utah's Museum of Natural History took over the dig, retrieving the well-preserved remains of the 90 kg skull. They were then able to match the skull with nose fragments and other skeleton fossils previously recovered from the surrounding wilderness.

Migration barrier

The experts speculate that the creature's head rolled into the bend of an ancient river, where it was partly buried. The right half of the head remained exposed to the river current, losing several bones before it was fully buried.

The scientists report their discovery in the Journal of the Linnean Society.

It is one of a dozen or more dinosaur fossils that have been recovered from this part of Utah – several of them entirely new species.

The fossils of closely related hadrosaurs have been found in the neighbouring regions of Montana and Alberta, Canada, suggesting that these creatures roamed over relatively small geographic areas, rather than migrating up and down North America in search of food as researchers once thought.

"There must have been a barrier – possibly physical, possibly ecological – that prevented them from migrating further afield," said Gates. "We just don't know what it was yet."