Brigham Young University scientists have uncovered further evidence of a possible dinosaur disaster 150 million years ago, in what might have been southern Utah's own version of the La Brea tar pits.

The latest proof of a catastrophe that killed hundreds or thousands of giant carnivorous dinosaurs came on the microscopic scale - that is, a scanning electron microscope examination of what is presumed to be an allosaurus egg.BYU researchers discovered the fossilized egg in 1987 at the Cleveland-Lloyd Dinosaur Quarry in Emery County. The egg has been dated, X-rayed, studied by computer imaging and examined by tiny core drillings.

It contains a tadpole-shaped dinosaur embryo. As reported nearly a year ago by the Deseret News, it is believed to be an allosaurus because its egg is about the right size and nearly all the bones discovered at the quarry are those of allosauruses. In fact, some allosaurus bones found nearby may be those of the mother dinosaur.

In the latest discovery, an electron microscope was used to find that another layer of shell was laid over the normal first layer of the egg.

Wade Miller, director of the BYU Earth Sciences Museum - which has been studying the egg for the past two years - said the second layer was "a pathologic or abnormal layer of shell . . . .

"We studied it and could see where the second layer covered up a lot of the pores of the first layer. It's known even now that some reptiles will do this."

If a reptile is under heavy stress or can't find a suitable nesting place, it may retain an egg in its reproductive tract until a good site shows up. If that happens too long, though, the reptile's body will add a second layer of shell material to the egg.

"This probably is what led to the death of the embryo," Miller said. The second layer covered the pores in the first, which "would seal the fate of the embryo, because it couldn't live once this oxygen supply was cut off."

That shows the mother allosaurus was ill or under stress.

Some scientists have interpreted the Cleveland-Lloyd quarry - now a desert on the edge of the San Rafael Swell - as an ancient dinosaur trap. For one thing, there are few remains of herbivores.

Of the thousands of bones discovered in the quarry, most are of the fierce allosaurus. But in every known fauna today, herbivores far outnumber the carnivorous animals.

So paleontologists interpret the scene as the margins of a lake, "probably a boggy, swampy area," Miller said.

At times, dinosaurs would get bogged down, make a lot of noise, and attract the local meat-eaters. The allosauruses would parade into the swamp, trying to get at the struggling victims, and become trapped themselves.

"In this case, I think the egg was inside the mother. She got trapped. This, therefore, was the stress."

She could have lived a couple of days while stuck in the deep mud, then died. Her body would have protected the egg until it could be fossilized.

"This would help explain why only one egg has been found (at Cleveland-Lloyd) even though over 10,000 bones have been found," Miller said.