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Dinosaurs grew in the egg in a similar fashion to modern birds, a study suggests. Scientists made the discovery after examining a cache of more than 200 fossilized bones from embryonic dinosaurs.
They were found strewn among fragments of eggshell and are all believed to belong to the same species, the 26-foot long-necked sauropod lufengosaurus. Crucially, the embryos were at different stages of growth, providing scientists with a rare opportunity to study how lufengosaurus developed before hatching.
Focusing on the femur, or thigh bone, they found evidence of rapid growth within the egg. Before hatching, the bones doubled in length from 12 to 24 millimeters, indicating a short incubation time.
Analysis of the bones' anatomy and internal structure showed that, as in birds, muscles became active inside the egg and helped shape the skeleton.
“This suggests that dinosaurs, like modern birds, moved around inside their eggs,” said lead scientist Robert Reisz, from the University of Toronto in Canada. “It represents the first evidence of such movement in a dinosaur.”
The findings, reported in the journal Nature, also revealed organic material inside the embryonic bones that may be fibers of collagen connective tissue. Reisz said, “We are opening a new window into the lives of dinosaurs.
This is the first time we've been able to track the growth of embryonic dinosaurs as they developed. Our findings will have a major impact on our understanding of the biology of these animals.”
The pieces of eggshell found are the oldest known from any land-dwelling vertebrate animal. It is the first time fragments of such delicate dinosaur eggs, measuring less than 100 microns thick, have been recovered in good condition.
The site, near Dawa in Lufeng County, lent its name to the dinosaur whose adult bones had been discovered there previously.
“A find such as the Lufeng bonebed is extraordinarily rare in the fossil record, and is valuable for both its great age and the opportunity it offers to study dinosaur embryology,” Reisz added.
“It greatly enhances our knowledge of how these remarkable animals from the beginning of the Age of Dinosaurs grew.”