updated 6/2/2005 5:28:01 PM ET 2005-06-02T21:28:01

The first known North American skulls of Cretaceous-era sauropods — big dinosaurs with little heads — have been uncovered in recent years by researchers at Brigham Young University and Dinosaur National Monument in Utah.

About a dozen sauropod skulls are known from the earlier Jurassic era, but these are the first in North America for the Cretaceous, the final 80 million years of the dinosaur period.

The four Cretaceous sauropod skulls or parts of skulls were found close to each other at the monument, which straddles the Utah-Colorado border.

"We've really got a remarkable — it's almost mind-boggling — new discovery," said Dan Chure, Dinosaur National Monument paleontologist. "If there's one thing you would not expect to find ... it's sauropod skulls, because they're so rare."

Also, the fossils have fine preservation, he said in a telephone interview with the Deseret Morning News. "It's kind of hard to overstate how amazing this is."

All four are the same type, a new species and genera, Chure said. They lived around 100 million years ago, or possibly a little earlier.

The new sauropod, which has not yet been formally named, may have been 25 feet long (7.6 meters long) with an 18-inch (45-centimeter) skull. In comparison, the apatosaurus, some specimens of which once were called brontosauruses, could exceed a length of 80 feet (24 meters).

Series of delicate bones
A sauropod skull is not a single bone but a series of delicate bones. "It seems that as soon as they die, the head falls off," Chure said. The bones fall apart and the pieces may wash downstream or become scattered by scavengers. They rot away because they are too thin to be easily fossilized.

Parts of North American sauropod heads had been recovered previously, but not full skulls.

Brooks Britt, assistant professor of geology at BYU, said, "Sauropod skulls are among the rarest of dinosaur finds because they have the thinnest bones, the most delicate skulls."

In the 1970s, visiting paleontologists discovered the site where the sauropod skulls were later uncovered, which is on the Utah side of the monument in the general vicinity of the visitors center.

About 2000, monument dug up the first preserved, articulated (not separated in pieces) skull.

"It's slightly distorted, but it's certainly an outstanding specimen," Chure said.

Extracting bones from slab
About a year and a half ago, crews dug out a giant slab of sandstone from the quarry, because they could see traces of fossilized bones in the rock. The slab was around 6 or 7 feet long (2 meters), 4 feet wide (1.2 meters wide) and 3 feet (90 centimeters) thick. It weighed thousands of pounds.

It was taken to the visitors center, and then last year was transported to BYU in Provo.

Britt's team extracted sauropod body bones and the second skull, which was disarticulated, meaning the pieces had fallen apart. They found the snout of a third sauropod of the same species, and at the quarry, scientists recovered the brain case of a fourth.

More specimens may await discovery in the quarry.

The articulated skull is so well-preserved that eventually it may be used to make a mold, which could be cast. The cast could be placed on display.

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