How dinosaurs grew to be as large as they did has always been a bit of a mystery. Now a new fossil discovery in Yunnan province in China is shedding some light on that question.

The find in China appears to be of bones and eggshells of nests from a dinosaur called Lufengosaurus. Dino nests were built on the ground, and the specimens appear to have been caught up in a flood during the Jurassic Period nearly 200 million years ago. The little bones of embryonic dinos are jumbled together, mixing specimens of a number of individuals.

Lufengosaurus was similar to some of the dinos you may have learned about as a child. It was a long-necked plant eater. Lufengosaurus and its relatives fall into the group that paleontologists call sauropodomorphs. One of their distinguishing characteristics is their enormous size.

Robert Reisz of the University of Toronto is the lead author of a study published in the journal Nature earlier this year about the Lufengosaurus remains. Discussing sauropodomorphs he said, “They were the biggest things that lived in the neighborhood.”

Lufengosaurus, for example, was about 9 yards long from head to tail, making the animal almost long enough to be awarded a first down on a football field. While not the largest animal that ever lived by a long shot, Lufengosaurus was the biggest animal in what’s now China at the time that it strode through history.

The new Lufengosaurus discovery is a mixture of hundreds of little dino bones representing animals that were developing inside their eggs. The fossils are from animals at different stages of development. Reisz and his colleagues have studied the bones, including 24 femurs. The biggest femurs were twice the size of the smallest ones, indicating the dinos were growing significantly even before the eggs hatched.

Inside the femurs was a space for blood vessels and tissues. The new research shows that those spaces were unusually large, useful for high rates of growth.

The research team also has beamed especially powerful X-rays at the fossils. They are hopeful that those results show there are organic remains inside the embryonic bones. I say “hopeful” because it’s still possible any organic remains are a byproduct of contamination after the bones were laid down in the Earth.

Lots of good dino discoveries have come out of China in recent years. Stay tuned for more information flowing from fresh finds like the embryonic remains of Lufengosaurus.