One of the world’s most amazing Cretaceous fossil beds, formed approximately 125 million years ago, in what is now northeastern China.
Researchers believe that the diverse people of this ancient community were suddenly buried by a devastating volcanic flow of hot ash and rock.
But the volcanic doomsday scenario, also known as China’s Cretaceous Pompeii, did not occur, researchers claimed on November 3. Proceedings of the National Academy of Sciences. The researchers say the animals found in these rocks, including nonavian dinosaurs, birds, mammals, insects, frogs, and turtles, were buried in their place. an unfortunate but not catastrophic series of events.
These Cretaceous rock formations, known as the Yixian Formation, are famous for two types of fossils. Although flattened, the fossil has impressively preserved details such as feathers, pigments, soft tissue, and even the contents of its stomach. These feather details helped eventually convince paleontologists that modern birds evolved from theropod dinosaurs (SN:99/9/18).
In the new study, researchers used highly accurate geochemical dating techniques to collect fossil-bearing rocks and fossils from two dinosaurs originally excavated from the site and now housed in a museum. A small zircon mineral was analyzed. According to paleontologist Scott McLennan of the University of the Witwatersrand in Johannesburg and his colleagues, these dates suggest that both Yixian fossil beds are less than 93,000 years old, which is a fraction of a geological time difference. It has become clear that.
However, the two types of fossils did not form at the same time. That means a single catastrophic event did not occur to all organisms, the researchers said. Drilling cores at several different locations in the Yixian Formation revealed that the 3D fossils lie beneath older, flattened fossil-bearing rock layers. A layer of hardened lava lies between the two.
From these analyses, the team devised a new hypothesis for how all these creatures died. Instead of a dramatic, sudden mass death, the researchers say, the Yixian Formation represents a “brief snapshot of normal life and death in early Cretaceous continental communities.”
3D fossils include skeletons such as: Psittacosaurus It seems that other dinosaurs are also in the nest (SN: November 16, 2016). Researchers previously discovered that the strikingly lifelike poses of these fossils were buried in the searing ash and rock of the ancient Italian city of Pompeii, which was devastated by the eruption of Mount Vesuvius in 79 AD. It has been pointed out that the posture is reminiscent of the posture of humans who were discovered (SN: February 4, 2014. SN: 8/7/24). That, and the presence of volcanic debris in fossil-bearing rocks, suggests that such pyroclastic flows may have buried these organisms.
New research should not be buried under the volcanic flow. Psittacosaurus They live in burrows and are buried when the burrow collapses. The sediments immediately surrounding and within the fossils were finer-grained than the surrounding rock. The researchers hypothesize that this may mean that there was a cavity in the rock formed by the dinosaur’s body. Over time, as the remains decayed, small grains of sediment seeped in, filling the voids and surrounding the skeleton.
As for volcanic evidence, the researchers say these fossil-bearing rocks contain some volcanic debris, but no evidence of violent pyroclastic flows. Furthermore, the poses of many of the creatures suggest sleeping positions rather than fighting or fear, and as one would expect from being caught in a fast volcanic flow and tumbling down multiple times, they were crushed to pieces. There is no evidence of bones.
Although the three-dimensional fossils formed in a terrestrial environment, the rocks surrounding the flat fossils indicate that they were buried in deep, fine-grained lake sediments, McLennan and colleagues say. Analysis of Earth’s orbital fluctuations, known as Milankovitch cycles, suggests that the timing of these dinosaur deaths coincided with intervals of heavy rain. The creatures may have died and flowed into the lake, where they were quickly buried by a thick layer of sediment. Such rapid burial means a low-oxygen environment ideal for preserving fossils. Careful preservation of details in these fossils, such as traces of feathers, also belies the extreme thermal conditions caused by volcanic flows, the researchers say.
Not all researchers are convinced. Zhang Baoyu, a paleontologist at China’s Nanjing University who has previously worked on the Yixian fossils, does not believe the researchers’ claim that the fossils were not buried by a pyroclastic flow has been proven. , says.
“The core findings of this paper…conclude that the sedimentation rate is: [when the fossils formed] It was very expensive,” Jiang said. But that doesn’t necessarily mean volcanic activity wasn’t the main cause, he said, and the team’s study only analyzed two separate specimens, which isn’t enough to draw that conclusion. added.
However, McLennan and colleagues argue that it is a logical fallacy that an amazing bone bed must have an amazing origin. Volcanic debris at the scene – tuff fragments, hardened ash and other volcanic rocks – may have given researchers a whiff of the culprit behind the deaths.
