New Dinosaur|jon_downes||05/10/05 at 13:07:09|jon_downes|xx|0||CHICAGO (Reuters) - A fossil found in South Dakota is that of a never
before seen species of dinosaur, a horse-sized plant eater with spikes
on its bony flat head, scientists said on Monday.
"When my colleagues saw a CAT scan of the new fossil, they tore up their
family tree diagrams and said, 'Back to the drawing board!' ... We never
suspected such a creature existed," said paleontologist Robert Bakker.

Discovery of the flat-headed member of the pachycephalosaur family
changes the view of dinosaur history during the final days of the
Cretaceous Period 66 million years ago, showing that family trees were
still evolving even as the entire dinosaur world was about to go
extinct, the Children's Museum of Indianapolis said in announcing the find.

The nearly complete pachycephalosaur skull was donated to the museum by
three amateur fossil hunters from Iowa who found it in 2003 while
exploring the Hell Creek Formation in central South Dakota.

The discovery was announced in Indianapolis in conjunction with the
annual meeting of the American Association of Museums.

The museum said the pachycephalosaur family is marked by dragon-like
heads covered with horns, knobs and bumps. The most famous family
member, Pachycephalosaurus, had a solid, domed bone helmet up to eight
inches (20 cm) thick used to ram other dinosaurs in their sides, it said.

The new species has a flat head with no bone dome. The only other
flat-headed pachycephalosaurs discovered were found in China and
Mongolia but all of those had had short muzzles and no long horns
anywhere on the skull, the announcement said.

The pachycephalosaurs in general all had massive necks and could inflict
significant "blunt force trauma" on other dinosaurs, Bakker said.

"This new species ... likely pressed their foreheads together and shoved
one another really hard," he added.

The museum, billed as the largest of its kind in the United States, said
the fossil would become part of its dinosaur exhibit.