Early Dinosaurs Were Social and Lived in Herds – May Have Been Key to Their Success

A new study of a huge fossil site in Patagonia shows that some of the earliest dinosaurs lived in groups, and that this behavior may be one of the keys to dinosaurs’ success. At ESRF, the discovery of embryos of the same species in fossil eggs contributed to this result.

In the past, studies have shown that some dinosaurs that existed in the last stage of the dinosaur age (Cretaceous) lived in groups. However, a big unresolved question is when and how this behavior appeared in its evolutionary history.

Mussaurus patagonicus Dinosaur Nesting Site
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 behavior may have been one of the keys to the success of dinosaurs. Credit: Jorge Gonzalez

In the early 2000s, an international team of scientists discovered a dinosaur nesting site 190 million years ago, which also contained juvenile bones belonging to the Patagonian ape, a primitive herbivorous sauropod dinosaur (large The predecessor of the long-necked dinosaur). In Patagonia (Argentina). “Such a well-preserved site will definitely provide us with a lot of information about how the first dinosaurs lived,” explained Diego Boll, a paleontologist at CONICET who discovered the site.

One of the first objects that could reveal how dinosaurs lived was the eggs found at that location, and Pol wanted to know if they were laid by Mussaurus. Pol explained: “It is difficult to find fossil eggs, and even more difficult to find fossil eggs with embryos inside, because their fossilization requires very special conditions.” ESRF, the European Synchrotron, is the perfect tool to study this problem. Sample type: Paleontologist and former ESRF scientist Vincent Fernandez of the Natural History Museum in London said: “We use high-energy X-rays to prevent damage In the case of a sample, penetrate the sample and have a complete understanding of its internals.”

After a complicated journey from Argentina (not every day people carry dinosaur eggs between continents as hand luggage), Pol took 30 of the more than 100 dinosaur eggs found on the scene to ESRF, carefully using powerful X-rays Check them. “We spent 4 days scanning these eggs 24 hours a day,” Fernandez explained. “Although it was tiring, the exciting results boosted morale.” High-resolution CT scans revealed some Mussaurus embryos inside the eggs. Fossils, and show that all these fossils belong to the common breeding grounds of a single dinosaur species.

The researchers also studied the site itself. These fossils were found on multiple rock formations at the same location, indicating that Mussaurus returned to the same location in consecutive seasons to form breeding herds. Based on the sediments, scientists were able to infer that the nesting site was on the dry edge of the lake.

Mussaurus patagonicus Embryo CT Scan
Using X-ray imaging, the scientists scanned eggs to discover preserved embryo skeletons, which they used to confirm the fossils as members of the plant-eating dinosaur, Mussaurus patagonicus. Credit: Vincent Fernandez

A key aspect of the area is that dinosaur bones are not randomly scattered throughout the fossil site, but are grouped according to their age. Small dinosaur fossils are located near the nest. It was found that one-year-old children are closely related to each other, including a set of 11 bones in a resting position, which indicates that Mussaurus formed a school for young individuals. Adults and sub-adults often move in pairs or alone, but they are all within one square kilometer. In order to determine the age of these juvenile fossils, scientists conducted histological studies, that is, cut out a thin piece of bone and observe the bone tissue under a microscope. “The bones of these dinosaurs grow every year, as do the tree rings, so by calculating the growth cycle, we can infer the age of the dinosaurs,” Boll added.

All the research results show a well-organized group structure, and is the first record of this complex social behavior in early dinosaurs (it is 40 million years earlier than other dinosaurs with evolutionary social behavior). Scientists have compared these results with other fossil egg sites in South Africa and China, and believe that social behavior can be traced back to the time when the dinosaurs originated. “These are not the oldest dinosaurs, but they are the oldest dinosaurs that proposed group behavior. Mussaurus belongs to the first successful family of herbivorous dinosaurs, so we think that the offspring of these long-necked dinosaurs may be socialized and protected. Part of the reason why it’s so common on all continents,” Pol concluded.

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