Pictured above: Artistic illustration of a litter of Patagonian rat dragon chicks and adult parents.
In a Jurassic cemetery in Patagonia, Argentina, there are more than 100 dinosaur egg fossils and the bones of 80 Patagonia rats, ranging in age from cubs to adults. A new study has found that these dinosaur remains suggest that paleontological animals lived in groups as early as 192 million years ago.
The researchers say the findings are the oldest documented evidence of dinosaur gregarious life, suggesting that dinosaurs exhibited complex gregarious behavior 40 million years earlier than previously thought.
Diego Pol, a paleontologist at Argentina's National Council for Scientific and Technological Research and principal investigator of the aided research, said: "The cemetery also shows that the animals have an internal structure. For example, young dinosaurs play together in small circles and then die. It is rare to find preserved behavioral signs in dinosaur bones, but now we have evidence that complex social behavioral structures exist in dinosaur populations. ”
Pictured above: An artistic illustration of the breeding grounds of a herd of Patagonian rats, showing individuals of different ages, including newborns in nests, young dinosaurs, and adult dinosaurs.
Associate Professor michael M. A. Thompson of the Department of Biology at Adelphi University in New York Michael D'Emic said: "I would say this is one of the most important paleontological discoveries of the year. Having so many individuals in a fossil species, from embryo to adult, is very exciting. ”
Since 2002, Bohr and his colleagues have excavated a relatively small outcrop in the Red Lake formation in southern Patagonia, covering an area of about 1 square kilometer. This formation is famous for containing fossils of Tagonian rats, which are based on tiny hatched specimen fossils discovered in 1979 and were inappropriately given a scientific name meaning "rat lizard".
Over the years, Bohr's team has found fossils of more than 100 eggs and dozens of new Patagonian rat-dragon individuals. These specimens include dinosaurs from 6 different life stages, from embryonic to adult.
Previous studies have shown that the eggs laid by patagoniaratosaurs have a soft cortical shell that is likely to walk on all fours during infancy and switch to bipedal walking shortly after one year of age. But now, Bohr and his colleagues have enough evidence to prove that sauropods were a group of herbivorous long-necked dinosaurs.
As shown in the image above: A litter of 192 million-year-old Patagonian rat dragon fossil eggs has been found in southern Patagonia, Argentina.
Bohr's team hypothesized that social life began with the transition of sauropods from small dinosaurs to giant dinosaurs. For most of the Triassic period (252 million to 201 million years ago), dinosaurs were small, about the size of horses. But between 227 million and 208 million years ago, sauropods grew larger, changing their size by two orders of magnitude, the researchers wrote in the study. But they still lay very small eggs. In the case of Patagonian rat dragons, the newly hatched pups hatch from eggs the size of eggs and weigh 1.5 tons as adults, equivalent to the weight of a hippopotamus.
In other words, newly hatched Patagonian rat pups must grow to a huge size within a few years. "During this period, they need to eat a lot to grow, but they're not big enough to protect themselves, and they don't have survival skills," Bohr said. Therefore, living in a herd of beasts can actually protect you at a very fragile stage in your life. ”
At the site, paleontologists found flocks of eggs, a clue that the male or female of patagoniaratosaurs would dig holes and then use the females as nests. Pol said the nests had 8 to 30 eggs. X-ray computed tomography of 5 of the nests showed that the eggs were arranged in two to three layers, containing embryonic bones from Patagonian rats. He noted that the large number of eggs at the site suggests that it was once a common breeding ground for dinosaurs.
Pictured above: a 192 million-year-old fossil egg from patagonia in southern Patagonia, Argentina.
Other dinosaur groups at different life stages have also been found at the site, including 11 juvenile dinosaurs under 1 year old, 2 adult dinosaurs found together, and 9 near-adult dinosaurs. Perhaps Patagoniaosaurus lived in groups, but dinosaurs of different ages tended to move together.
These dinosaurs may have died from drought. Bohr believes that we know the place is seasonal and there are signs of drought in the sediment. Many animals die in a resting position, meaning they lie down and die, then covered in dust.
Emick said it's extremely rare to find so many well-preserved dinosaurs in one place. More interesting and important, the animals seem to live in social groups. People tend to think of extinct groups like sauropods as evolutionary "dead ends," but that doesn't mean they don't have advanced behaviors like society.
In fact, sociality may have played an important role in the evolutionary success of sauropods, the largest animals ever on Earth.