About 120 to 130 million years ago, northeastern China was home to a lush landscape filled with temperate forests, lakes, and diverse fauna. Today, this ancient ecosystem, preserved in the Yixian Formation, provides some of the world’s most exceptional fossils.
For decades, scientists believed that the preservation of these fossils was due to volcanic eruptions. They hypothesized that the eruptions quickly buried and preserved the organisms in layers of hot ash – similar to how Mount Vesuvius preserved the inhabitants of Pompeii in AD 79.
However, a new study refutes this hypothesis. The researchers argue that the remarkable preservation was actually due to more common processes, such as the periodic accumulation of sediments from seasonal rains and the collapse of animal burrows, which created oxygen-free environments conducive to fossilization.
Dating back to the age of dinosaurs, the Yixian fossils remained untouched until the 1980s, when villagers unearthed remarkably well-preserved creatures.
The Yixian Formation soon became famous for its unparalleled fossil finds. Unlike traditional fossils, which are often skeletal fragments, Yixian fossils have preserved delicate details such as feathers, fur, scales, internal organs and even stomach contents.
Some specimens are so well preserved that they depict animals in their last moments.
The Yixian Formation is a fossil goldmine
Among these treasures are the first known feathered dinosaurs, which have allowed us to deepen our understanding of how modern birds evolved from their dinosaur ancestors.
The study used advanced techniques to date the fossils more precisely than ever before. The researchers determined that these fossils date from a condensed period of about 125.8 million years ago, spanning less than 93,000 years.
This time span suggests that rather than a series of volcanic events, the fossils were preserved over a relatively short period under stable conditions.
Paul Olsen, co-author of the study and a paleontologist at Columbia University’s Lamont-Doherty Earth Observatory, believes the new findings highlight a common human tendency to assume “extraordinary causes for ordinary events.”
Rather than being the result of dramatic volcanic incidents, fossils reflect normal die-offs within an ecosystem, captured in exquisite detail by natural sedimentation processes.
Sediment accumulation or volcanic eruption?
Contrary to the volcanic catastrophe theory, the Yixian fossils show no signs of the extreme conditions typical of pyroclastic flows, which are known to twist bodies into a posture characteristic of intense heat.
In contrast, many Yixian fossils are preserved with the animals’ limbs attached to their bodies, suggesting that they may have been undisturbed and even asleep at the time of their death.
The team hypothesizes that periodic rains accelerated sediment accumulation, particularly in lake environments, where the lack of oxygen further slowed decomposition. This process preserved not only the skeletons but, in some cases, the soft tissues as well, he writes InterestingEngineering.
The study also suggests that burrow collapse may have contributed to preservation. Large dinosaurs, whose remains are entirely absent from Yixian, may have destabilized the ground as they moved, causing sudden collapses that buried smaller animals alive.
While this new understanding improves the story at Yixian, Olsen believes there could be similar fossil finds elsewhere, particularly in regions that once had similar environmental conditions. In the United States, for example, sites in North Carolina, Connecticut, and New Jersey have yielded well-preserved fossils in the past, but none on the same scale as Yixian.
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Source: www.descopera.ro
