Two complete dinosaur skeletons Psittacosaurus from one of the sites analyzed by the research team. Some scientists say that these fossils show evidence of preservation because the burrows collapsed.
Liu Jun
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Liu Jun
For decades, a few hundred miles northeast of Beijing, the Yixian Formation has provided an impressive treasure trove of dinosaur fossils from the early Cretaceous period (about 145 to 66 million years ago).
“It gives us an extraordinary window in the month and goes to this time where there are different dinosaurs,” he says Paul Olsenearth scientist at Columbia University. “We’re looking at a snapshot of this ecosystem.”
Most researchers say that the remarkable preservation of many of these specimens is due to volcanic activity. But in the research published in the journal PNASOlsen and his colleagues argue an alternative explanation – that, over time, the burrows collapse, suffocating people. This will happen over and over for 90,000 years.
“There’s no way this detracts from this beautiful fossil,” Olsen said. “In fact, to me, it makes it even more amazing that we’re getting such a deep view of diversity millions of years ago.”
Nanjing Institute of Geology and Paleontology team at a site where many three-dimensional dinosaur fossils have been excavated.
Paul Olsen
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Paul Olsen
Chinese Pompeii?
The Yixian Formation has yielded a stunning array of fossils over the years. “It produced the vast majority of feathered dinosaurs in China,” Olsen said. These flattened fossils are well preserved.
There are also all the 3-dimensional fossils of carnivorous dinosaurs and plant-eating dinosaurs, “which includes animals as far away as triceratops,” Olsen said. “He was complete to the very last bone. And he was often in a position where he looked like he was frozen in the morning.
This is seen, combined with deposits rich in volcanic ash, which has led many researchers to conclude, “that the animals were catastrophically entombed by either volcanic mud flows or killed by volcanic ash or some sort of great accident,” said Olsen.
But this is not true for Olsen. He describes the people who died in Pompeii when Mount Vesuvius erupted and quickly buried the city. “He was in a really contoured position that tells us he was very uncomfortable when he died,” Olsen said. “They all came together and put their hands together.”
Many dinosaur fossils have been found in this area of China, but they seem to be sleeping peacefully. There were no signs of discomfort due to the fiery volcanic activity.
Paleontologists also found clutches of baby dinosaurs clustered together. “How can these animals stay together if they are surrounded by such a huge mass of matter?” asked Olsen. “It’s not a mystery what happens to organisms when they get caught in these things. They tear them apart.”
A different view
Olsen and his colleagues studied the sediments around and inside two three-dimensional fossils from Psittacosaurus. “The sediment inside the animal in both dinosaurs was finer than the sediment outside,” he said.
These observations showed Olsen that the animals were buried with their skin and muscles intact, as the flesh only allowed the fine grain material to flow slowly into the body cavity, filtering out anything gross. Olsen and his colleagues argued that the burial would not have been the result of a dangerous volcanic flow. He said the collapse of the burrow was an easier conclusion.
“Maybe some of them collapsed because the big sauropod dinosaurs were running,” Olsen said. “Or there could be an earthquake. Or maybe it’s just waterlogged mud just collapsing.”
Olsen said other animals are also buried in the sediment at the bottom of the deep lake. No volcanic activity is required there.
But some researchers are skeptical of the new assessment.
“Good paper,” he said Baoyu Jiangpaleontologist at Nanjing University who was not involved in the research. “But they only analyzed two dinosaur fossils. They didn’t even study the fossils in the lake.” Olsen disputed this, explaining that he and his colleagues analyzed ash samples from lake sediments.
Jiang found the results uncertain and speculative. “Sometimes you find fossils in normal sediments like they were found,” he said. “But in general, the feathered dinosaurs, they were closely preserved with volcanic ash. There are various possibilities.”
For Olsen, take away immediately.
“We must be careful in our efforts to understand the deep past so as not to create stories that include extraordinary catastrophic events,” he said, “when, in fact, simple ordinary people can explain the same thing.”
