Fossilized dinosaur (representational image) Wikimedia commons

Researchers from Nanjing University in China have finally unlocked the mystery behind the mass fossilisation of animals that lived about 120 million years ago in Jehol Biota.

Back in Cretaceous age, these creatures were instantly killed by massive volcanic eruptions, which preserved fossils of their torched bodies, researchers have found.

Jehol Biota, an ancient northern China ecosystem, has mystified scientists for long. Researchers have been perplexed about how a wide variety of animals including dinosaurs, mammals, early birds and fishes were buried and preserved together as if in mass graves.

Researchers have clarified that the animals were burned and petrified by hot molten lava and ashes from massive volcanic eruptions.

"All the studied fossils are directly embedded within pyroclastic flows. And the preserved animals are characterised by entombment poses and showed evidence of charring," Baoyu Jiang, who led the study, told the BBC.

"What we're talking about in this case is literal charring, like somebody got put in the grill."
- George Harlow, co-author of the report

The flora and fauna from early Cretaceous period are huddled together and so well preserved in Jehol that the vast collection has significantly contributed to scientists' understanding of the era, the research paper, which was published in Nature Communications, said.

'What we're talking about in this case is literal charring, like somebody got put in the grill," George Harlow, one of the co-authors of the report, told the Daily Mail.

Though it was already known that the animals had died of a mass mortality event of volcanic eruptions, the new insight offered by the study suggested that charred bodies were together transported by the lava into low-lying volcanic lakes, where they were fossilised.

".. the authors go a step further in suggesting that all the Jehol animals were killed, transported and exceptionally preserved by the pyroclastic flows [lava]," said Professor Mike Benton, a palaeontologist from University of Bristol.

The view that held sway previously was that most animals lived around the basin and were swept into the lakes by gushing waters.

However, the team notes that even though fish fossils have also been recovered from the area, only terrestrial animals such as dinosaurs, mammals, and birds appeared scalded.