The famous Utah dinosaur fossil egg is continuing to make paleontologic history. Now it's thought to be the only known egg of an allosaurus.

If so, it may indicate the allosaurus - Utah's state fossil - gave birth to live young.Recent computer enhancement of X-ray CAT scans taken of the dinosaur egg seem to confirm that it indeed does carry a polliwog-shaped embryo. This was suspected back in February, when the CAT scan device at American Fork Hospital was used on the egg.

The fossil was discovered by Brigham Young University scientists last September at Cleveland-Lloyd Dinosaur Quarry in Emery County, a national natural landmark at the border of the San Rafael Swell.

"We feel 90 percent sure that there's something in there," Wade Miller, director of the BYU Earth Sciences Museum, said Wednesday. "We're still running tests on it."

He and Karl Hirsch of the University of Colorado are writing a paper about the rare find. It will be presented to a symposium in Montana, where an amazing number of other fossil eggs have been discovered.

Dee Hall of BYU discovered the Utah egg in a matrix of the 150 million-year-old Morrison Formation, as dated by two methods, called potassium-argon and fission track dating.

"The surrounding area has yielded bones before," Miller said. In fact, the allosaurus bones there are what made experts think this may be an egg of that fearsome carnivore.

"We can't say for sure on this, but I think the chances are much better than not of its belonging to an allosaurus." All previous dinosaur eggs have been from herbivores.

Not only would this be the world's only known meat-eater dinosaur egg, but it is "the oldest one (egg) from the whole northern hemisphere," Miller said.

At first, scientists were not certain whether the rock really was an egg. "We did not know for sure until Karl Hirsch had looked at it under an electron microscope and studied the detailed cellular structure," he said.

"The shell is there."

Last week a BYU team returned to the site and "cut out a block of matrix, and they're starting to cut through that now." The scientists hope to find other eggs, although most likely there are none, he said.

Still, they did find more fragments of the original fist-sized egg, and it's possible another egg or two will turn up in the block of matrix.

Miller and Hirsch had decided independently, after careful study of the computer recreations, that this might be an egg from a reptile that gave birth to live young.

"There seems to be a very good chance that the egg was one retrained in the mother rather than laid in the ground," he said. As with some present-day reptiles, the eggs hatch inside the mother and the young are born live.

If that's the case, Ms. Allosaurus must have died with the unhatched egg inside. In fact, the embryo only had the chance to form for a few days before something killed it.

"The embryo's so young there's no bone development yet," Miller said.

Today the cracked, semi-squashed egg shows it has been distorted by pressure. Possibly many tons of rock and earth pressed down on it over millions of years. In addition, it was broken open not long after the egg was formed.

Mud poured inside and flowed around the embryo, carrying it to the botto, of the shell, where it was fossilized.

Experts are planning to make a chemical analysis of material in the egg near the embryo, and further field work may take place at the quarry.

BYU researchers also plan to return soon to Dry Mesa, Colo., where fossils of the largest land animal - a mega-dinosaur - were discovered a few years ago.