Rare find: a teething dinosaur embryo.

Rare find: A teething dinosaur embryo

Last summer, geology student Rodney D. Scheetz peered through a microscope at fossil remains he had unearthed a few weeks earlier in Colorado, and found a paleontological surprise: 135- to 150-million-year-old fragments of a dinosaur embryo, the oldest yet reported in the Northern Hemisphere.

The Brigham Young University undergraduate found tiny embryonic foot bones, vertebrae and jawbone fragments of a gazelle-like, herbivorous dinosaur called Dryosaurus altus. Lower jaw pieces held two baby teeth, each roughly 1 millimeter wide, that had barely emerged past the jawbone -- a sign that they belonged to an embryo just about ready to pop out of its shell, Scheetz says. Officials at Brigham Young, located in Provo, Utah, announced the discovery Sept. 21.

Judging from its well-developed bones, "the little guy that was curled up in the egg must have died just before it could hatch," Scheetz adds. By studying fossilized embryos, scientists can learn whether baby dinosaurs stayed in their nests or left after hatching and can glean clues to how dinosaurs cared for their young.

D. altus is only the seventh dinosaur species for which embryos have been recovered, says Philip J. Currie of the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta. Worldwide, scientists have unearthed fewer than 100 dinosaur embryos, he says. Most of these date back 65 to 100 million years.

While working in the fossil-rich Morrison Formation near Uravan, Colo., Scheetz also found dinosaur eggshell shards and the remains of eight individual dryosaurs ranging from hatchlings to young adults. The finds may shed some much-needed light on early dinosaur development -- in this case, how the dryosaur, which measured about 12 inches long as a fully developed embryo, matured into a 10- to 13-foot-long adult. Scheetz hopes for "a broader and better picture as far as what's going on with elementary growth in dinosaurs -- how fast they grew and what kind of strategies they used in family life."

The excavated area may have been a nesting site for a herd of dryosaurs, says Wade E. Miller, director of Brigham Young's Earth Science Museum. To find out, Scheetz plans further screening of his fossils and a return to the site next spring.