Baby dinos pumped their muscles inside the egg

JURASSIC life was fast and furious even before dinosaurs made it out of the egg. A rare clutch of fossil dinosaur embryos suggests they grew at record rates and flexed their muscles in preparation for life on the outside.

Long-necked sauropods grew to gigantic size, but we know little about how they got so big. Robert Reisz at the University of Toronto Mississauga in Canada and his colleagues have found 200 tiny dinosaur bones in Jurassic rocks from Yunnan Province, China. They are probably unhatched embryos of Lufengosaurus, which is a close relative of the sauropods, and grew up to 9 metres long (Nature, DOI: 10.1038/nature11978).

The bones appear to have been riddled with blood vessels, meaning the tissues were burning oxygen ? and growing ? rapidly. "If the embryonic growth rate extends to hatchlings and juveniles, these [dinosaurs] grew very, very fast," says Reisz.

The structure of the bones also suggests the tiny dinos were flexing their legs in the egg to strengthen their muscles ? the earliest evidence of embryonic bodybuilding in the fossil record.

This article appeared in print under the headline "Baby dinos pumped their muscles"

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