[Paleopsych] NYT: The Dinosaur That Walked on Two Legs May Have Started Life on Four

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Fri Jul 29 15:48:33 UTC 2005

The Dinosaur That Walked on Two Legs May Have Started Life on Four


    For several years scientists have been finding 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 is being reported today in the journal
    Science by a team of paleontologists headed by Robert Reisz of the
    University of Toronto.

    The fossils were actually 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 an egg that was
    less than three inches long. The scientists identified the embryos as
    belonging to a long-necked, short-tailed, plant-eating dinosaur called

    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 15 feet 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.

    Dr. Reisz and his colleagues came to this surprising conclusion from a
    detailed examination 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," Dr. Reisz said.

    Dr. 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 reproduced
    and, in at least one case, started life on four legs and grew to be
    two-legged animals.

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