Scientists have struck gold in the badlands of Argentina: a vast dinosaur nesting site that has provided the first unequivocal embryo bones from a class of large dinosaurs and the first definite fossil skin from any dinosaur embryo.
CBS News Correspondent Elizabeth Kaledin reports that researchers literally stumbled upon thousands of fossilized eggs, some rare embryos, and, for the first time ever, fossilized dinosaur skin.
"It's a moment I'll never forget," said Lowell Dingus of the American Museum of Natural History. "To walk out of the vehicle and just take five minutes to walk out on the flats and see everybody kneeling down and picking up chunks of dinosaur eggs."
The surface of the square-mile site in Patagonia is littered with dark-gray fossil fragments of round, rough-textured, six-inch eggs.
"You see eggshells everywhere," said Luis Chiappe of the American Museum of Natural History in New York, co-leader of the expedition that found the site last November. He and other scientists report the discovery in Thursday's issue of the journal Nature.
The embryo remains appeared inside fragments of eggshell. The discoveries should shed light on the early development of sauropods, a class of plant-eaters with long necks and tails, small heads, and four massive legs. The class included some of the biggest animals ever to walk the Earth.
The eggs were laid some 70 million to 90 million years ago, apparently by titanosaurs that grew about 45 feet long, not very big by sauropod standards. The hatchlings might have been only about 15 inches long.
Paleontologists speculate the eggs were laid near a river that flooded, suffocating the eggs and burying them in deep layers of mud and sediment.
From the embryonic remains, "we're really getting a look at what these animals would have looked like to us, and felt like to touch, when they hatched," said Dingus.
The eggs contain the first-known embryos of the giant plant-eating dinosaurs called sauropods.
The remains help knock down a controversial suggestion that sauropods gave live birth. Additionally, they suggest that sauropods converged repeatedly in one place to lay eggs, which would explain the massive accumulation at the site.
Scientists "never had any real good evidence that's what dinosaurs would do," said Kenneth Carpenter of the Denver Museum of Natural History, who is familiar with the report.
The find shows that a particular kind of large round dinosaur egg found in Africa, India, China, Europe, and South America is from sauropods, at least in many cases. Though sauropods were proposed as the source of the eggs, the new find solves a 100-year-old mystery.
"If you're a dinosaur paleontologist, then I think it's a pretty exciting and wonderful discovery," Carpenter said.
Chiappe said scientists found embryonic remains witin so many eggshell fragments that it appears some catastrophe struck the nesting ground. Floods may have penetrated the porous shells and drowned the embryos, he said.
The fossilized embryonic bones look like tiny light brown flakes surrounded by green mudstone in eggshell fragments. No complete embryo skeletons were found, but discovering even the collapsed bones is very unusual. Before the new find, embryonic remains had been identified from only five species of dinosaur.
Scientists recovered 70 or so shell fragments containing dark pieces of fossilized skin in fingernail-sized patches or smaller. The scales are clearly visible.
Analysis of embryo remains might indicate how quickly sauropods grew within the egg, and perhaps how fast hatchlings grew, Chiappe said. As more remains from different stages of development are found, scientists might get clues to the pattern of bone formation and development in the embryo, he said.
The site is in Neuquen, a province in northwestern Patagonia.