Early dinosaurs were sociable and moved in herds 193 million years ago - 40 million years earlier than first thought, a new study has revealed.
More than 100 eggs, complete with embryo remains still inside, have been dug up at a dinosaur graveyard in the Laguna Colorada Formation in Patagonia, Argentina, providing the world's first evidence of herd behaviour.
Scans show they belong to the same species - a primitive long necked herbivore called Mussaurus patagonicus, according to the team of palaeontologists from the Massachusetts Institute of Technology.
The shells, with embryos inside, date back 193 million years to the Mesozoic Era, about 40 million years earlier than previous estimates of the start of herd behaviour.
Fossilised bones of 80 juveniles and adults were also dug up, grouped by age across an area of about half a square mile on the dry margins of a lake.
Eggs and hatchlings were in one area, adolescents nearby and grown ups scattered throughout - typical of a complex, social structure, the team said.
New research on a vast fossil site in Patagonia shows that some of the earliest dinosaurs, the Mussaurus Patagonicus, lived in herds and suggests that this behaviour may have been one of the keys to the success of dinosaurs
Scientists use ESRF high-energy X-rays to penetrate in the eggs without destroying it and get a full view inside it, discovering embryos of Mussaurus Patagonicus
The dinosaurs worked as a community, laying their eggs in a common nesting ground, according to study co-author Dr Jahandar Ramezani.
Youngsters congregated in 'schools,' while adults roamed and foraged for the herd.
'This may mean the young were not following their parents in a small family structure,' said Dr Ramezani.
'There's a larger community structure, where adults shared and took part in raising the whole community.'
The eggs are about the size of a chicken's egg, and using state of the art X-ray imaging, the team were able to examine the contents without breaking them apart.
Within the eggs they found remarkably well preserved embryos that allowed them to confirm the identity of Mussaurus patagonicus.
The plant-eater reached up to 20 feet long and weighed over a ton. It lived in the early Jurassic and is a member of the sauropodomorphs.
They were the forerunners to Brontosaurus, Diplodocus and other massive sauropods - the biggest animals that ever roamed Earth.
The fossils indicate a communal nesting ground and adults who foraged and took care of the young as a herd, according to Dr Ramezani, who said: 'To borrow a line from the movie "Jurassic Park" - dinosaurs do move in herds.
'And they lived in herds 40 million years earlier than the fossil record showed.'
The international team including experts from Argentina and South Africa have been excavating the ancient sediments since 2013.
Living in herds may have given Mussaurus and other
