Baby dinosaurs likely twitched inside their eggs to exercise developing muscles and spur bone development, according to a new study of the oldest embryonic dinosaur remains ever discovered.
With a few rare exceptions, almost all known dinosaur embryos are from the Cretaceous period, which ended 65 million years ago. But scientists recently discovered hundreds of fossilized dinosaur embryo bones in China’s Lufeng County (map) that date to the lower Jurassic period and are between 190 and 197 million years old.
“These are by far the oldest embryonic [dinosaur] materials,” said study leader Robert Reisz, a paleontologist at Canada’s University of Toronto Mississauga.
“[But] we did not find complete eggs,” Reisz noted. “It’s a bone bed, which means the bones have been sorted and concentrated, and all of the eggshell materials have been broken up into little pieces.”
When Reisz and his colleagues examined the fossils, they looked very porousâ€”a telltale sign that they belonged to developing embryos. “One of the characteristics of embryonic bone is that it looks very pockmarked because it’s growing very fast and the tissue surrounding it is penetrating the bone extensively with blood vessels,” he explained.
In an analysis published today in the journalÂ Nature, the team concluded that all the bones belonged to a single species of long-necked, plant-eating creature in the genusÂ Lufengosaurus, which grew to a length of about 30 feet (9 meters) and was a common dinosaur in the region.