For several years scientists have been fin-ding fossilized embryos of dinosaurs from 80 million to 100 million years ago. They have now uncovered several 190-million-year-old dinosaur embryos, the oldest ever found.
The discovery was reported on Friday in the journal Science by a team of paleonto-logists headed by Dr Robert Reisz of the University of Toronto. The fossils were excavated in 1978 in South Africa, but it has taken this long to expose the embryos from the surrounding rock and eggshell and then interpret the tiny remains.
One of the best preserved embryo skeletons was still curled up inside the egg, less than 5cm long. The scientists identified the embryos as belonging to a long-necked, short-tailed, plant-eating dinosaur called Massospondylus. They were relatively common in what is now South Africa in the beginning of the Jurassic period. All previous dinosaur embryos have been from the Cretaceous period, which ended 65 million years ago.
As adults, these creatures reached lengths of more than 4.5m and were able to walk on two legs. Yet the new research suggested that their hatchlings began life moving about on all fours, the scientists reported.
Reisz and his colleagues came to this surprising conclusion from a detailed exa-mination of the horizontal neck, heavy head and limb proportions of two well-preserved embryo skeletons.
This appeared to mean that the young were quadrupeds and somehow matured into bipeds, a pattern of development, they said, that was almost unheard of among vertebrates.
"The results have major implications for our understanding of how these animals grew and evolved," Reisz said.
Reisz, a professor of biology, was joined in reporting the research by other Toronto scientists and dinosaur experts at the National Museum of Natural History of the Smithsonian Institution and the University of Witwatersrand in Johannesburg. James Clark, a paleontologist at George Washington University, who was not involved in the research, said the discovery was "exciting in providing a major piece of the puzzle" of how large plant-eating dinosaurs repro-duced and, in at least one case, started life on four legs and grew to be two-legged
animals.
The researchers also reported that the body proportions of the embryonic skeletons and an absence of well-developed teeth "suggest that hatchlings of this dinosaur may have required parental care."
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