How can we explain the extraordinary preservation of dinosaur and mammal fossils from the Yixian Formation in China, which leads us directly to a rich Cretaceous ecosystem? If we thought until now that dramatic volcanic episodes were to blame, a new study suggests that the explanation may be much less catastrophic.
It is called the “Chinese Pompeii”. Located in the northeast of China, it contains an extraordinary paleontological site. On a large scaleOn a large scale An incredible number of fossils from the Lower Cretaceous (between 120 and 130 million years old), which present a truly remarkable state of preservation.
Since the 1990s, numerous fossils of dinosaurs, birds, insects, turtles, frogs have been found. MammalsMammals Excavated from the Yixian Formation, some contained fossilized remains of skin, limbs or feathers. Many specimens found at the site have thus become archeological references of great scientific value. This is also where the first Non-Avian DinosaursNon-Avian Dinosaurs The owner of the feathers has been identified. The quality of preservation of the feathers was so high that scientists were able to identify their original colors!
But how can we explain such incredible preservation of fossils?
Fossilization, not such an easy process to perform.
As a reminder, FossilizationFossilization It is a relatively difficult process to perform and requires very specific conditions to prevent the entire body from rapidly decomposing. Compared to the number of dead dinosaurs, only a small fraction have seen their remains preserved by mineralization, allowing these bones to survive for tens, or even millions, of years.
It is generally necessary to bury the carcass soon after the death of the animal and that the environmental conditions are anoxicanoxicThat is, very poor in oxygen. The environment must then remain stable for a very long time to allow the mineralization process to complete. Some environments are therefore more favorable for producing good-quality fossils: for example, when an animal fell into a lake and was quickly covered. SedimentSedimentswhen the body was washed away during a flood and covered with a thick layer of mud, or when it was quickly buried under ash. Volcanic eruptionVolcanic eruption.
The frozen scenes of life are reminiscent of the Pompeii disaster.
The quality of fossils from the Yixian Formation has also led scientists to suspect that violent and sudden volcanic episodes are at their origin. A bit like the catastrophe that destroyed Pompeii in AD 79. The main argument supporting this idea was the presence of several perfectly articulated skeletons formed in continental environments, such as this fossilized scene of a fight between a mammal and a small dinosaur, which seems to have been frightened at the time. Several such catastrophic events would have occurred over a period of about 1 million years. Fossil siteFossil site extremely rich.
No disaster, but normal mortality in a favorable environment
However, a new study published in the journal PNAS came against the assumption that had become firmly entrenched in recent years. A team led by Scott McLennan from the University of the Witwatersrand in South Africa has actually done detailed dating of various fossils. ZirconZircon found in the sediments in which they were embedded. Their dating MineralsMinerals It revealed that the fossils were dated to 125.8 million years ago and that various animals had died over a period of 93,000 years. And in all that time, nothing catastrophic had happened!
However, studies show that ClimateClimate It was particularly humid in this region of the world at that time. Conditions that wash large amounts of sediment to the bottom of lakes quickly bury dead organisms and allow them to be preserved. There is no evidence for the researchers. Pyroclastic flowPyroclastic flow or a volcanic eruption has occurred. In this case, these two extreme violent manifestations would certainly have destroyed the corpses to a great extent, they would have been quickly buried, but in a coherent manner and neither wings nor limbs. will be preserved.
Small dinosaurs and mammals that suffered from burrowing.
On the contrary, many animals have died among them. to sleepto sleepwithout causing any destruction, their pose was interrupted. For scientists, there is therefore only one explanation for these observations:to fallto fall The bill in which these small mammals or dinosaurs took shelter. A hypothesis confirmed by grain-size analysis of the sediment surrounding the skeleton.
” What was said about protection? [de ces fossiles] to measure the lightthe light An important human bias, explains one of the authors in a press release. When we do not understand their origin, we attribute extraordinary causes, miracles to ordinary events. These fossils are only a snapshot of daily mortality. General conditionsGeneral conditions Over a relatively short period of time » !
