The truth about the world's top 'dinosaur gold mine' in China

Scientists have just discovered what makes Yixian, a world where dinosaurs seem to have frozen in time .

Yixian is an early Cretaceous formation in northeastern China , known to the world as the "Pompeii of dinosaurs" because it preserves the world's top quality fossil specimens.

In most places around the world, dinosaur skeletons are mostly exposed as fragmented bones, missing many pieces, badly damaged, pressed against a flat rock slab.

However, in Yixian, dinosaurs were discovered with completely intact 3D skeletons, keeping the exact posture when alive, even with part of the soft tissue intact.

Two of the dinosaur skeletons excavated from Yixian are extremely rare intact 3D fossils - (Photo: Chinese Academy of Sciences).

According to Live Science, the previous popular hypothesis about the formation of Yixian was a volcanic disaster as powerful as the one that engulfed the ancient Roman city of Pompeii 2,000 years ago.

In Pompeii, the tremendous amount of ash from the eruption of Mount Vesuvius killed everyone and everything almost instantly and "petrified" them in their final positions.

But now, new evidence suggests that the "Pomeii of dinosaurs" may have formed in a different way.

A paper published in the scientific journal PNAS suggests a less serious cause: The dinosaurs may have been buried in collapsed caves.

To find evidence, scientists analyzed zircon samples taken from some of the best fossil specimens.

Zircon is a mineral that commonly forms in volcanic and fossil rocks, retaining uranium as it forms while rejecting lead. Uranium is radioactive and slowly decays into lead over millions of years.

By measuring the ratio of uranium to lead in zircon , scientists determined that the fossils in the Yixian Formation were deposited rapidly from about 125.8 million years ago.

But this happened over a period of just 93,000 years, much shorter than previously thought.

During this time, three wet weather events caused sediment to accumulate in the lake and on land much faster than expected.

This causes many dead organisms to be quickly buried, and the oxygen that normally promotes decomposition is blocked.

This effect is most pronounced in lakes, where sediment accumulates so rapidly that soft tissues can be preserved in fine detail.

According to paleontologist Paul Olsen from the Lamont-Doherty Earth Observatory at Columbia University's School of Meteorology (USA), the lead author, this scenario is much more feasible than the hypothesis that the dinosaurs were engulfed by fast-flowing volcanic mudflows.

'Mud flows are extremely violent and are capable of tearing apart any living or dead creatures in their path,' Dr Olsen explained.