A James Cook University researcher has helped unearth a 190-million-year-old dinosaur nesting site in South Africa, the oldest nesting site for dinosaurs ever found.
The discovery, of the prosauropod dinosaur Massospondylus, at an excavation site in South Africa, has revealed significant clues about the evolution of complex reproductive behaviour in early dinosaurs.
Led by University of Toronto (Mississauga) palaeontologist Robert Reisz, with co-author Dr Eric Roberts from JCU and a group of international researchers, the study describes clutches of eggs, many with embryos, as well as tiny dinosaur footprints.
It has provided the oldest known evidence that the hatchlings remain at the nesting site long enough to at least double in size.
The eggs are approximately five centimetres wide and seven centimetres long and the embryonic dinosaur skeleton is about five to six centimetres long and an estimated four centimetres tall in the egg.
They can grow up to about five metres in length and about two metres tall.
According to the authors, the newly unearthed dinosaur nesting ground is more than 100 million years older than previously known nesting sites.
Dr Roberts, Senior Lecturer in JCU’s Discipline of Geology, said the sediments were an incredible source of information about the life and times of early dinosaurs.
“Clues recorded in the rock, such as the tracks of the hatchling dinosaurs, traces of ancient ripples and evidence desiccation cracks all suggest that these animals were nesting in a dynamic shoreline environment with fluctuating climate conditions,” he said.
“Ultimately, the preservation of these exquisite fossils appears to be tied to episodic flooding that buried parts of the nesting colony multiple times over unknown generations.”
Dr Roberts said more than 10 nests had been discovered at several levels at the site, each with up to 34 round eggs in tightly clustered clutches.
“The distribution of the nests in the sediments indicate that these early dinosaurs returned repeatedly, known as ‘nesting site fidelity’ to this site, and likely assembled in groups or colonial nesting to lay their eggs, the oldest known evidence of such behaviour in the fossil record.”
The large size of the mother, at six metres in length, the small size of the eggs, about six to seven centimetres in diameter, and the highly organised nature of the nest, suggested that the mother may have arranged them carefully after she laid them, he said.
“The eggs, embryos, and nests come from the rocks of a nearly vertical road cut only 25 metres long,” said Dr Reisz, head of Vertebrate Paleontology at the University of Toronto.
“Even so, we found 10 nests, suggesting that there are a lot more nests in the cliff, still covered by tonnes of rock. We predict that many more nests will be eroded out in time, as natural weathering processes continue.”
The fossils were found in sedimentary rocks from the Early Jurassic Period in the Golden Gate Highlands National Park in South Africa. The site has previously yielded the oldest known embryos belonging to Massospondylus, a relative of the giant, long-necked sauropods of the Jurassic and Cretaceous periods.
The study, co-authored by Drs. David Evans (Royal Ontario Museum, Canada), Eric Roberts (JCU, Australia), Hans-Dieter Sues (Smithsonian Institute, USA), and Adam Yates (University of the Witwatersrand, South Africa), was published on January 23 (Toronto, US time) in the Proceedings of the National Academy of Sciences.