New species of duck-billed dinosaur found

Scientists have discovered the fossil of a new species of duck-billed dinosaur in US that roamed the Earth about 79 million years ago.

The dinosaur species, first uncovered and documented by a professor at Montana State University (MSU), showcases an evolutionary transition from an earlier duck-billed species to that group's descendants, researchers said.

The new species neatly fills a gap that had existed between an ancestral form with no crest and a descendant with a larger crest, providing key insight into the evolution of elaborate display structures in these gigantic extinct herbivores.

Elizabeth Freedman Fowler and MSU paleontologist Jack Horner named the dinosaur Probrachylophosaurus bergei and suggest it is a previously missing link between a preceding species, Acristavus, which lived about 81 million years ago, and later form Brachylophosaurus, which lived about 77.5 million years ago.

"The crest of Probrachylophosaurus is small and triangular, and would have only poked up a little bit on the top of the head, above the eyes," said Fowler.

The other bones in its skull are very similar to those of Acristavus and Brachylophosaurus, Fowler said. However, Acristavus does not have a crest; the top of its skull is flat, while Brachylophosaurus has a large flat paddle-shaped crest that completely covers the back of the top of its skull.

"Probrachylophosaurus is therefore exciting because its age - 79 million years ago - is in between Acristavus and Brachylophosaurus, so we would predict that its skull and crest would be intermediate between these species. And it is," Fowler said.

"It is a perfect example of evolution within a single lineage of dinosaurs over millions of years," said Fowler.

During the summer of 2007, Fowler was leading a crew from the Museum of the Rockies in excavating a bed of Earth near the town of Rudyard in north central Montana.

The site contained fossils of duck-billed dinosaurs. A visiting school group discovered bones poking out of an old quarry. Horner recognised that some of the new bones were parts of a skull, which is the most crucial part of the skeleton for identifying the species.

"The first bones we uncovered were the pelvis and parts of the legs; which were so large it led to the site being given the nickname 'Superduck,'" Fowler said.

After returning to the lab, Fowler and Horner discovered they had most of the skull and postcranium of a new kind of dinosaur.

A nearby site also showed a fragmentary juvenile of the transitional Probrachylophosaurus, which suggests that successive generations of the Brachylophosaurus lineage grew larger crests by changing the timing or pace of crest development during growth into adulthood. The research was published in the journal PLOS ONE.