August 2, 2005
Oldest Dinosaur Eggs Ever Found Held Babies
WASHINGTON -- Unhatched dinosaur eggs dating back 190 million years carried fully developed embryos that would have been born clumsy and helpless, scientists said on Thursday.
Their finding, published in Friday's issue of the journal Science, suggests even the earliest dinosaurs tended carefully to their young. It also raises questions about how the giant four-legged dinosaurs called sauropods evolved.
"These animals do not have any teeth, and since they are ready to hatch, that is strange," said Robert Reisz of the University of Toronto at Mississauga in Canada, who led the study.
"The only explanation for that is they must have been fed by the mother. That would be oldest evidence of parental care in the fossil record," Reisz added in a telephone interview.
"We are looking at the very beginning of dinosaur evolution."
"It does support the idea that parental care and possible altricial (helpless) young existed throughout the reign of the Dinosauria," paleontologist Jack Horner of Montana State University agreed in an e-mail.
The eggs come from a dinosaur called Massospondylus, one of a group called prosauropods that later evolved into the giant sauropods such as apatosaurus, previously known as brontosaurus.
"Most dinosaur embryos are from the Cretaceous period (146 to 65 million years ago)," Reisz said in a statement.
The fossil eggs were found in South Africa in 1978, but scientists have only now been able to open and study them properly. Reisz's team used tiny tools to do it.
"We have essentially miniature jackhammers. They are pencil sized," he said.
"And we use very delicate dental tools."
Working under a powerful microscope, Reisz's team had to design a vibration-free table to work on.
"When somebody slammed a door in the building, my technician who preparing this felt that," Reisz said.
When they got the eggs open, they could see the baby dinosaurs were just about to hatch. In fact, egg fragments were all around, suggesting that at least one did.
And the babies did not look like the parents. Adult prosauropods were slender and two-legged.
The babies looked more like the dinosaurs that developed later, and they looked like the babies of animals such as birds and mammals, as opposed to the small but adult-proportioned young of reptiles.
"The head is quite large. The pelvic girdle is very small. That's where most of the muscles that would be used for locomotion are located," Reisz said.
"So we are suggesting this was a relatively helpless little hatchling."
Very few animals develop as this one appears to have, Reisz said.
"It starts out as a quadruped and becomes, as it grows up, as a biped. There are very few examples in nature that do this," he said.
One example, however, is a human baby.
"We start out as an awkward quadruped and we manage to become bipedal," he said.
Now the researchers can use computers to work out how these animals grew from a 6-inch (15-cm) long embryo into a 15 foot-(5-meter) long adult.
"This discovery is exciting in providing a major piece of the puzzle of how sauropodomorphs grew and reproduced," said biologist James Clark of George Washington University in Washington.