- Paleontologists found 100 eggs and 80 skeletons from a dinosaur called Mussaurus on a nesting site in Patagonia.
- The fossils were grouped in clusters of adults and adolescents, suggesting that Mussaurus lived in flocks.
- The nesting site is 193 million years old, making it the earliest evidence of dinosaur herds.
A 193-million-year-old nesting site containing more than 100 dinosaur eggs increases paleontologists’ understanding of an early dinosaur species.
Research published Thursday describes a collection of eggs and young and adult skeletons from a dinosaur called Mussaurus patagonicus, which was found in Patagonia, Argentina. The dino is an ancestor of long-necked herbivores called sauropods, such as Brachiosaurus.
Most of the chicken sizes were discovered in clusters of eight to 30, suggesting that they resided in nests as part of a common breeding ground. Researchers also found Mussaurus skeletons of similar sizes and ages buried together. Together, these patterns provide evidence that the dinosaurs lived in flocks.
“I went to this site with the goal of finding at least one lovely dinosaur skeleton. We ended up with 80 skeletons and more than 100 eggs (some with embryos preserved inside!)” Diego Pol, researcher at the Egidio Feruglio Paleontology Museum in Patagonia and lead author of the new study, Insider said via email.
He called the place “one of a kind”.
Prior to this discovery, scientists believed that shepherding behavior was limited to dinosaurs that came much later, in the very late Jurassic and Early Cretaceous periods. This is because the earliest fossil evidence for sauropod herds dates back only 150 million years. However, this nesting site pushes this timeline back more than 40 million years. It is the earliest known evidence of social groups among dinosaurs, the study authors said.
X-rays give a look into fossilized dinosaur eggs
Argentine paleontologists discovered the first Mussaurus skeletons at this Patagonian site in the late 1970s. The dinosaurs they found were no more than 6 inches long. Unaware that they had uncovered newborns, the researchers named the creature “mouse lizards” because of the small size of the skeletons.
Pol decided to re-explore the area from 2002, and by 2013 he had helped find the first adult Mussaurus fossils there. These bones revealed that adult versions of these “mouse lizards” were closer to today’s hippos. They grew to weigh about 1.5 tons and reached lengths of 26 feet from nose to tip of tail. But infants could fit in the palm of one hand.
Since then, Pol’s team has also uncovered and examined the contents of the nesting site, which measures just under half a square kilometer. In 2017, he took 30 of the eggs to a laboratory in France, and his group then used X-ray technology to look inside and confirm the nature of the embryos without breaking the shells.
By analyzing the sizes and types of bones in the nesting site, the researchers determined that the animals were buried near colleagues of a similar age. Some clusters had young ones less than a year old, others consisted of individuals who were slightly older but not yet fully grown, and finally there were smatterings of adults who had died alone or in pairs.
That type of age division, the researchers said, is a key sign of herds: Young people hung out with others their age, while adults looked for food and protected society.
“They rested together and probably died during a drought,” Pol said. “This is compatible with a herd that stays together for many years and within which the animals come close to each other to rest, or to feed or do other daily activities.”
Another strong indication of herd behavior is the nest site itself: If Mussaurus lived as a community, it would make sense for them to lay eggs in a common area.
Living in flocks may have helped Mussaurus survive
To find out the age of the fossils, researchers examined minerals in volcanic ash scattered around eggs and skeletons, and determined that the fossils were about 193 million years old.
Previously, scientists believed that this type of dinosaur lived at the end of the Triassic period, about 221 million to 205 million years ago. But the new date suggests instead that Mussaurus thrived in the early Jurassic period. This, in turn, is proof that Mussaurus’ ancestors survived a mass extinction 200 million years ago.
The key to that survival, the study suggests, may have been their shepherding behavior.
“They were social animals and we think this could be an important factor in explaining their success,” Pol said.
Common life has probably helped Mussaurus find enough food, perhaps by making it easier for them to feed over larger areas.
Mussels of the same size would likely “group together to coordinate their activities,” Pol said as larger adults and smaller cubs moved at different speeds.
He added that given the size difference between newborns and adults, it probably took these dinosaurs many years to reach full size. So the young clam could have been vulnerable to predators.
By staying in herds, adults could better protect their young.