An international team of researchers, including a paleontologist from the University of Bonn, have proven dinosaur embryos to be the oldest ever found. The specimens of Lufengosaurus discovered in China lived during the lower Jurassic about 200 to 190 million years ago.

Based on the bone tissue, Dr. Koen Stein was able to show that the fossils must have been in a very early stage of development. The rapid growth and high reproductive rate of these Chinese dinosaurs is astounding. The results are now being presented in the renowned scientific journal "Nature".

Rice fields - as far as the eye can see. However, in recent years, construction projects have inflicted some scars upon the lush green area in the vicinity of Dawa in Southern China. Luckily for science: During excavation work, some tiny bones were unearthed in a layer of marl.

"It was natural to suspect that they were the remains of dinosaur embryos", says Dr. Koen Stein of the Steinmann Institute for Geology, Mineralogy, and Paleontology of the University of Bonn.

Especially since the remains of adult Lufengosaurus had already been found in the area. The positioning of the little vertebrae and other bones - just a few millimeters long - indicated that these were nests of eggs of these dinosaurs.

Little research so far on Lufengosaurus
Lufengosaurus lived in the Lower Jurassic about 200 to 190 million years ago and is thus one of the oldest dinosaurs, which have been studied comparatively little.

The animals had a long neck and a total body lentgh of about eight meters. Lufengosaurus walked at least part of the time on two legs and had sharp teeth and claws - but nevertheless probably was a herbivore.

An international, interdisciplinary team of scientists from Canada, Taiwan, Australia, and China, together with the paleontologist at the University of Bonn, have now studied whether the little bones found at Dawa are really Lufengosaurus embryos.

Cavities in vertebrae provide information on the state of development
Dr. Stein of the University of Bonn specializes in paelohistology, which studies the tissues of fossil organisms. Under the microscope, he examined thin sections of several vertebrae - just a few millimeters long - which came from about 20 embryos in different stages of development. The vertebrae are criss-crossed by channel-like cavities.

Dr. Stein: "They held the blood vessels, which supplied the growing bone tissue with nutrients". In young animals, which are growing rapidly, these cavities are particularly large. In more slowly growing older animals, these channels narrow, because it is no longer necessary to supply so many nutrients and more and more necessary to strengthen the bone. From the size of the cavities in the vertebrae, therefore, it is possible to extrapolate the animal's stage of development.

An analysis of characteristics helped classify the fossils
The vertebrae examined by the paleontologist at the University of Bonn had particularly large cavities. "Based on this snapshot of their development, we were able to determine that the fossils must have been dinosaur embryos in an early stage of development", reports Dr. Stein. This finding is supported by the remains of egg shells and by fossilized cartilage in the interior of the vertebrae.

Lead author Dr. Robert R. Reisz, Professor at the University of Toronto Mississauga (Canada), compared the specific features of the embryo fossils to the characteristics of various dinosaurs. He came to the conclusion that the nests of eggs at Dawa come from a dinosaur group that also includes Lufengosaurus, which has been found there often.

"We are opening a new window into the lives of dinosaurs", says Prof. Reisz. "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".

Rapid growth and frequent reproduction
"We have thus identified the oldest dinosaur embryos ever found", says Dr. Stein. Furthermore, the researchers have been able to show that Lufengosaurus grew very rapidly and reproduced frequently. Taken together, these two things gave the dinosaurs an advantage in selection and explain why they apparently spread so far around the globe.

Publication: Dinosaur embryology: inside the bones of an Early Jurassic sauropodomorph from China, scientific journal Nature, DOI: 10.1038/nature11978