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Argentine Eggs Bear Embryonic Dino Tissue

The first fossils of embryonic dinosaur skin are among the treasures from a huge nesting ground in Argentina, described today in New York City at a joint press conference of the American Museum of Natural History (AMNH) and the National Geographic Society. The trove includes softball-sized eggs containing the first-ever bones and teeth of unhatched plant-eating dinosaurs called sauropods.

Dinosaur embryos were first found in Montana in the 1980s. All five known embryo types belong to a group of birdlike dinosaurs called the theropods. But last year, AMNH vertebrate paleontologist Luis Chiappe and his colleagues from the Museo Municipal Carmen Funes in Neuquén, Argentina, unearthed a sixth kind of embryo. While searching for dinosaur fossils in Patagonian badlands near Auca Mahuida, Argentina, they came across a square-mile covered with fragments from hundreds of thousands of dinosaur eggs. "You walk on a surface that is littered with eggshells," says Chiappe.

Digging into the outcrop, the team found more than a dozen intact eggs and the remains of nearly 40 embryonic dinosaurs. While no embryo was complete, the researchers did recover enough bones for a composite skeleton. The bones and tiny pencil-shaped teeth strongly suggest that the creatures were sauropods, which reached tens of meters long in size as adults. Some patches of scaly skin, preserved as what Chiappe calls "a perfect replica," have patterns that resemble the adult skin of titanosaurs. A report on the discoveries will be published later this week in Nature and featured in the December National Geographic.

The discovery could help reconstruct the early development of sauropods, fleshing out changes in bone tissue and skeletal proportions. "You can't talk about life history without babies," says paleontologist Jack Horner of the Museum of the Rockies in Bozeman, Montana. "Embryos are the best, of course, because that's the starting point."