CT scan unscrambles rare, ancient egg. (Paleontology).

A tangled heap of bones and bone fragments found inside an ancient bird egg may soon be reassembled thanks to high technology--and scientists won't even have to crack open the egg to do it.

Huge flightless birds called elephant birds strolled their Madagascar homeland until they went extinct about 400 years ago. Believed to be the heaviest birds that ever lived, they weighed half a ton and were about 3 meters tall. Their eggs were the largest single cells in the animal kingdom and could hold about 7.5 liters of material.

When researchers at the University of Texas at Austin recently performed a computerized tomography (CT) scan of an unbroken elephant bird egg, they discovered a tiny, dismembered skeleton. Amy M. Balanoff, a vertebrate paleontologist at the school, constructed digital models of individual bones. Using the rapid-prototyping techniques common in the automotive and aerospace industries, she then made three-dimensional plastic copies of the bones.

So far, Balanoff has made three-times-life-size copies of about 100 bone fragments. After making similar copies of the few remaining fragments, she'll assemble a replica of the embryo. Balanoff estimates that the embryo was about 70 percent of the way to hatching when it died inside the eggshell. By comparing its stage of development with that of embryos of ostrichlike emus, Balanoff estimates that elephant bird eggs took 47 days to hatch.

Future CT scans of other intact elephant bird eggs may reveal embryos at other stages of development, Balanoff notes. Analyzing a series of embryos should give scientists a better understanding of how the elephant bird grew so large. --S.P.