Persons and colleagues Philip Currie and Mark Norell detailed their findings in Friday's issue of the journal Acta Palaeontologica Polonica.

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"They give us an unprecedented look into the very early embryology of these developing dinosaurs, " said paleontologist Mark Norell at the American Museum of Natural History in New York, who wasn't involved in the find.

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Mark Norell, a prominent paleontologist at the American Museum of Natural History in New York who didn't participate in the study, said he doesn't know if the upright-posture myth is as widespread as the new study indicates.

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