Parts of sauropod headgear had been recovered from this continent, however. BYU researchers found some brain cases earlier at another site in Utah but not full skulls.

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

Recently, he and his lab teased the second skull and the snout of a third specimen from a large block of sandstone sent there from the monument. Also recovered was the brain case of a fourth animal.

The second skull was disarticulated, meaning the pieces had fallen apart. But the bones were there, and they are especially valuable because they can be examined from all sides.

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 monument visitors center. In the 1980s, said Chure, "we relocated the site and collected some bones that were sticking out of the ground and weathering."

The following decade, monument staff members worked at the quarry. About the year 2000, they dug up the first stunning find, the beautifully preserved and articulated skull.

By articulated, paleontologists mean it is together, not separated in pieces. "It's slightly distorted, but it's certainly an outstanding specimen," Chure said.

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, 4 feet wide and 3 feet thick. It weighed thousands of pounds.

"It was a whoppin' big block," Chure said.

It was lifted from the quarry by helicopter and taken to the visitors center. Early last year, a truck carried the slab to BYU, where Britt's team worked on it, painstakingly removing rock.

They extracted sauropod body bones and essentially a whole second skull, which was in pieces.

"Those guys did an amazing job," Chure said. "Some of the bones are paper thin, and they got all of the bones out of the rock."

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 new quarry. "The producing layer goes for probably at least as long an area as the quarry we have inside the building, and we've only excavated a small part of it," Chure said.

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.

How did four skulls end up together? Chure can't tell for certain.

The remains were in an ancient river or stream environment. Perhaps a herd of the animals drowned crossing a river. Or maybe they died in a drought, waiting beside a river that had gone dry, and a later flash flood washed the carcasses together.

He doesn't know what else might be discovered at the new site.

"We could have used up all our luck right away," he said. But he doesn't really think that and quickly adds that there's a lot more digging and chipping to do.

"Further work there is likely to turn up additional specimens," he said.

Chure hopes that he and Britt can get funding to support a concerted, longer effort. The new quarry, he said, might turn out to be as important as the famous one at the visitors center.

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E-mail: bau@desnews.com