Unscrambling the Past

By Frederic Golden

It was an atypically peaceful scene for those dino-eat-dino days. Amid the shallow streams of a broad floodplain, scores of huge, grazing female dinosaurs were making their nests and hovering near their eggs, as their predecessors had doubtless done for ages untold. But their tranquillity was suddenly disturbed. Out of nowhere came a flood of mud and silt, scattering the lumbering beasts and burying their progeny. The lively dinosaur nursery was lost forever.

Or nearly so. Some 80 million years after that late Cretaceous calamity--give or take 10 million years--its telltale remains have poignantly resurfaced. At a news conference in New York City last week, as well as in a report in Nature, scientists revealed that they had stumbled upon the site of the doomed dinosaur rookery during an expedition to remote badlands in central Argentina last November. Scattered over a square mile of parched Patagonian soil, they found the whole or shattered remains of thousands of grapefruit-size, fossilized dinosaur eggs--so many, in fact, that they couldn't avoid crushing them underfoot or with the wheels of their cars. "We were picking up eggs all over the place," says the American Museum of Natural History's Lowell Dingus, a geologist who is a leader of the expedition.

To scientists, the site is a paleontological field of dreams. The eggs include dozens of embryos--the first to be unearthed anywhere in the southern hemisphere (and an exponential jump in the existing worldwide inventory of only five specimens). What's more, the beautifully preserved bits and pieces include tiny (about a tenth of an inch long), pencil-shaped teeth and mosaics of precise, miniature, lizard-like scales. Says American Museum paleontologist Luis Chiappe, another of the team's co-leaders: "Finding dinosaur embryos is rare enough. Finding the [soft, perishable] tissue that surrounded those bones is truly spectacular."

An immediate result of the discovery is that it solves a lingering puzzle. Similar spherical eggs have been recovered elsewhere in South America as well as in Europe, Africa, India and China, but no one could tell for sure what sort of dinosaur laid them. After examining the bones and distinctively shaped teeth of the fragmented embryos, some of which were close to hatching when they died, the researchers firmly identified them as a type of sauropod, kin to the familiar Brontosaurus (more accurately known as Apatosaurus) of comic-book fame. Had they survived, they would have been about 15 in. long at birth--"about the size of a small poodle," says Chiappe--but 40 ft. to 50 ft. from the tips of their giraffe-like necks to the ends of their long, ground-hugging tails in adulthood. The third team leader, paleontologist Rodolfo Coria of Argentina's Museo Municipal Carmen Funes, identifies them more specifically as titanosaurs, smaller versions of sauropods that were common in the area.

The embryos lay to rest suspicions voiced by paleontological gadfly Robert Bakker that sauropods gave birth to live young--though the grinding wear patterns on the embryonic teeth hint that the little dinos probably did break out of their shells voraciously hungry. Under a microscope, the postage stamp-size patches of fossilized embryonic skin--the first ever found--turned out to have scales arrayed in distinctive patterns (rosettes, parallel rows) similar to the arrangement of the small bony plates on the backs of titanosaurs. This could mean, says Chiappe, that like modern crocodiles, the young sauropods grew body armor as they matured.

In the future researchers hope their bonanza will answer key questions about sauropod maternal behavior--whether, for example, the dinosaur moms laid their eggs haphazardly or carefully arranged their nests to protect them from meat-eating predators or the crushing feet of passing females. What seems clear, in any case, is that the herds of sauropods formed nesting groups, like the duck-billed maiasaurs ("good-mother lizards") discovered in western Montana by paleontologist John Horner of the Museum of the Rockies in Bozeman. "It's a survival strategy," says Horner, adding admiringly, "it would have been quite a sight!"

Confident that they will learn still more about creatures that ruled the earth unchallenged for more than 200 million years, Chiappe and his colleagues plan to return to their dinosaurian mother lode next March. Says Coria: "This discovery opens large doors that had remained closed for years." To make sure the site won't fall prey to contemporary egg snatchers, the provincial government has declared it a protected "paleontological park" and is keeping it under full-time guard.

--Reported by Andrea Dorfman/New York

With reporting by Andrea Dorfman/New York