Palaeontologists working in China have unearthed the earliest collection of fossilized dinosaur embryos to date. The trove includes remains from many individuals at different developmental stages, providing a unique opportunity to investigate the embryonic development of a prehistoric species.

Robert Reisz, a palaeontologist at the University of Toronto in Mississauga, Canada, and his colleagues discovered the sauropodomorph fossils in a bone bed in Lufeng County that dates to the Early Jurassic period, 197 million to 190 million years ago. The site contained eggshells and more than 200 disarticulated bones — the oldest known traces of budding dinosaurs, the researchers report online today in Nature1.

“Most of our record of dinosaur embryos is concentrated in the Late Cretaceous period,” says David Evans, curator of vertebrate palaeontology at the Royal Ontario Museum in Toronto. “This [study] takes a detailed record of dinosaur embryology and pushes it back over 100 million years.”