A 193-million-year old nesting ground with more than 100 dinosaur eggs offers evidence they lived in herds

Artistic reconstruction of a nest of Mussaurus patagonicus. Jorge Gonzalez
Paleontologists found 100 eggs and 80 skeletons of a dinosaur named Mussaurus in a nesting site in Patagonia.
The fossils have been grouped into groups of adults and juveniles, suggesting that Mussaurus lived in herds.
The nesting site is 193 million years old, making it the earliest evidence of dinosaur herds.
A 193 million year old nesting site with more than 100 dinosaur eggs turns paleontologists' understanding of an early species of dinosaur upside down.
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The research, published Thursday, describes a collection of eggs and juvenile and adult skeletons of a dinosaur named Mussaurus patagonicus found in Patagonia, Argentina. The dinosaur is an ancestor of long-necked herbivores called sauropods, such as Brachiosaurus.
Most of the chicken-sized eggs were discovered in groups of eight to 30, suggesting that they lived in nests as part of a common hatchery. Researchers also found mussaurus skeletons of similar size and age buried together. Taken together, these patterns provide evidence that the dinosaurs lived in herds.
“I went to this page to find at least one nice dinosaur skeleton. In the end, we found 80 skeletons and more than 100 eggs (some with embryos preserved in them!). ”Diego Pol, researcher at the Egidio Feruglio Paleontology Museum in Patagonia and the lead author of the new study, told Insider via email.
He called the site "unique".
Prior to this discovery, researchers thought that herding behavior was limited to dinosaurs, which came much later, in the very late Jurassic and early Cretaceous periods. That's because the earliest fossil evidence of sauropod herds is only 150 million years old. However, this nesting site shifts this timeline back more than 40 million years. It's the earliest known evidence of social groups among dinosaurs, the study authors said.
X-rays give an insight into fossilized dinosaur eggs
A fossilized mussaurus egg more than 190 million years old found in southern Patagonia, Argentina. Roger Smith
Argentine paleontologists discovered the first Mussaurus skeletons at this Patagonian site in the late 1970s. The dinosaurs they found were no longer than six inches. Little did the researchers know they had spotted newborn babies, and named the creature the "mouse lizard" because of the small size of the skeletons.
Pol decided to re-explore the area from 2002, and by 2013 he had helped locate the first adult mussaurus fossils there. These bones indicated that adult versions of these "mouse lizards" were closer in size to modern hippos. They grew to a weight of about 1.5 tons and reached a length of 26 feet from nose to tip of the tail. But infants could fit in the palm of a human hand.
A screenshot from a video showing how scientists like Diego Pol used high-energy X-rays to look inside a mussaurus egg without destroying it. Vincent Fernandez / Diego Pol / European Synchrotron
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Since then, Pol's team has also discovered and examined the contents of the almost 800 square kilometers large nesting site. In 2017, he took 30 of the eggs to a laboratory in France, and his group then used X-ray technology to look inside the embryos and confirm the nature of the embryos without breaking the shells.
By analyzing the size and type of bones in the nesting floor, the researchers found that the animals were buried in the vicinity of other animals of the same age. Some groups had pups that were less than a year old, others were made up of slightly older but not yet fully grown individuals, and finally there were a few adults who died alone or in pairs.
This type of age segregation, the researchers said, is a key sign for herds: adolescents clinging to others their age, while adults searching for food and protecting the community.
"They rested together and probably died during a drought," said Pol. "This is compatible with a herd that stays together for many years and in which the animals come close to each other to rest, forage or other daily activities."
Another strong indicator of herd behavior is a nesting site itself: if mussaurus lived as a community, it would make sense for them to lay eggs in a common area.
Herding life may have helped Mussaurus survive
Nest with mussaurus eggs found in Patagonia more than 190 million years ago. Diego Pol
To find out the age of the fossils, the researchers examined minerals in volcanic ash that was scattered around the eggs and skeletons and found that the fossils were about 193 million years old.
Previously, scientists thought that this type of dinosaur lived during the Late Triassic, about 221 million to 205 million years ago. But the new date instead suggests that Mussaurus thrived during the early Jurassic period. This, in turn, is evidence that the ancestors of Mussaurus survived a mass extinction 200 million years ago.
The key to this survival, the study found, could have been their herding behavior.
"These were social animals and we think this could be an important factor in explaining their success," said Pol.
Artist's impression of the nesting site of a Mussaurus herd in what is now Argentina. Jorge Gonzalez
Community life likely helped Mussaurus find enough food, perhaps by making it easier for them to forage in larger areas.
Mussaurs of the same size would likely "band together to coordinate their activities," Pol said, since larger adults and smaller juveniles moved at different speeds.
He added that given the size difference between newborns and adults, it likely took many years for these dinosaurs to reach full size. So the young mussaurus could have been prone to predators.
By staying in herds, adults could better protect their young.
Read the original article on Business Insider

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