How ancient lethal volcanic gas left a gift for paleontologists

Deadly pyroclastic flows from volcanic eruptions 130 million years ago helped exquisitely preserve the creatures of northeastern China's Jehol Biota.

Nanjing University/Baoyu Jiang
The typical entombing poses of the Jehol terrestrial vertebrate fossils (a, Psittacosaurus, a ceratopsian dinosaur; b-c, Confuciusornis, a primitive crow-sized bird). This boxer-like pose is typical of victims of pyroclastic flows, resulting from the postmortem shortening of tendons and muscles.

The fossilized remains of birds, dinosaurs, lizards, and plants have been preserved in China's Jehol biota so remarkably that one can even find signs of delicate bones and feathers. 

Researchers now say they know how these organisms were preserved so well over the past 130 million or so years. According to research published in the multidisciplinary journal Nature Communications, pyroclastic flows – the currents of hot gas and rock moving hundreds of miles per hour that accompany some volcanic eruptions – cooked, transported, and then mummified them.

“Pyroclastic flows are lethal, have occurred throughout time and, based on these findings, could be responsible for the preservation of other fossil groups that are closely associated with ash deposits,” said George Harlow, a curator in the Museum’s Department of Earth and Planetary Sciences and an author of the paper, in a press release. “The fresh, hot, dry volcanic ash promoted burning, charring, or mummifying of soft tissues, which, as a result, became more resistant to decay and better preserved.”

The ash obtained from the fossil bed was fine grained and shielded the organism in a way that prevented degeneration, Jin Meng, a curator in the American Museum of Natural History’s Division of Paleontology and an author on the paper, told the Monitor.

Evidence of charring points toward a similarity between the preservation mechanism among vertebrates at the Jehol site and the victims of Pompeii and Herculaneum, Italy, who were killed during the 79 AD eruption of Mount Vesuvius, say researchers. 

“Excavation work in [Jehol] has uncovered exquisitely preserved specimens ranging from plants and insects to fishes and non-avian dinosaurs,” said Dr. Meng in the press release.

“This study provides an alternative mechanism on how organisms, particularly terrestrial species that presumably occupied different niches, can be preserved with aquatic and tree-dwelling taxa in sediments in such a form of completeness,” said Meng.

It was earlier known that volcanic eruptions caused the death of the creatures in the fossil bed. But this paper sheds light at the mechanisms that helped in the preservation of the creatures, says Meng.

So far, the Jehol Group has yielded some 60 species of plants, nearly 1000 species of invertebrates and 140 species of vertebrates (fishes and tetrapods), states The University of Bristol.

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