Washington Scientists have uncovered the oldest dinosaur embryos ever found, dating to the beginning of the Jurassic age 190 million years ago.
The find, which has taken years to decipher, is helping them understand the development of a long-necked, plant-eating giant called Massospondylus carinatus.
The discovery is producing three important results, Robert R. Reisz, of the University of Toronto at Mississauga, said in a telephone interview.
The first, he said, is the "gee whiz, Guinness world record that we have found the oldest dinosaur embryo. That's cool and they are beautiful."
The second is the hard science, Reisz said. Scientists are now able to look at the growth pattern of the animal from embryo to adult because they now have skeletons from various states of its life and can compare changes as the animal grew.
The third area, he said, is most speculative. Some of the embryos were clearly ready to hatch, he said, but they have no teeth, "and that suggests to us that some form of parental care was required : not just protecting but active feeding."
The report by Reisz and others at the University of Toronto, the Smithsonian Institution's National Museum of Natural History and the University of the Witwatersrand, South Africa, is published in today's issue of the journal Science.
James Clark of George Washington University in Washington, who was not part of the research group, concurred that these are the oldest dinosaur embryos yet found.
"The importance of the discovery is that they are from a primitive member of the sauropodomorphs, a large group that includes the largest land animals that ever lived. Sauropodomorph embryos are rare, and the only previously known embryos of this group, from Argentina, are from a much later and more specialized form," Clark said.
The find enables researchers to study the animal's growth and development because they now can compare skeletons at different ages.
"Surprisingly, the proportions of the limbs, neck and head suggest that as a baby and young animal this species walked on four legs, but as an adult it was able to walk on two legs some of the time. This kind of change in posture hasn't been documented in any other dinosaur," Clark noted.
Indeed, Reisz and colleagues reported that the Massospondylus hatchling was born four-legged with a relatively short tail, a horizontally held neck, long forelimbs and a huge head. As the animal matured, the neck grew faster than the rest of the body but the forelimbs and head grew more slowly. The end result was a two-legged animal that looked very different from the four-legged embryo.
Reisz suggested the change from four- to two-legged could be a matter of balance related to the development of the animal's neck.
An adult Massospondylus could grow more than 15 feet long.
The dinosaur eggs were discovered in South Africa in 1978 during road building in the Golden Gate Highlands National Park, but had not come under study until three years ago, when Reisz's team began to analyze them.
The research was funded by the University of Toronto, the Natural Sciences and Engineering Council of Canada, the National Geographic Society and the Paleo-Anthropology Scientific Trust of South Africa.