Researchers at Nanjing University have solved the mystery behind the formation of 120-million-year-old animal graveyard in China. Researchers claimed that volcanic eruptions that took place more than 120 million years ago buried and sealed the animals similar to the victims of vicious explosion that destroyed the Roman City of Pompeii.

Researcher Baoyu Jiang said that pyroclastic flows emitted from a series of volcanic eruptions is believed to have choked and enclosed the creatures from the lower Cretaceous era close to the volcanoes, resulting in the formation of the fossil beds in Liaoning province in north-east China.

"Scientists have been curious for a long time in how these animals were killed and became exceptionally preserved," Jiang said.

For the study, Jiang compared the 14 well-preserved and burnt fossils from five bone beds from Jehol, China - including the crow-size bird Confuciusornis and the parrot-faced dinosaur Psittacosaurus - with remnants from the Roman victims of the 79 A.D. eruption of Mount Vesuvius. Besides the fossils, the researchers also examined the ashy sediments across the region to explain the preservation and buildup of the fossils.

The researchers found that ash encasing the fossils is similar to those seen in other massive volcanic eruptions including the 1883 eruption of the Indonesian volcano Krakatoa. While closely examining the fossils, the researchers observed carcasses with their limbs extended and spiderweb cracks in their bones. These visible characteristics were also noticed in victims of other pyroclastic ash eruptions and Pompeii.

"The authors go a step further than had been done before in suggesting that all the Jehol animals were killed, transported and exceptionally preserved by the pyroclastic flows," said paleontologist Michael Benton of the U.K.'s University of Bristol, in an email to National Geographic. "This is quite a challenge to previous views that assumed most of the animals lived in and around the lakes in which they are found."

However, Benton does not believe that the pyroclastic flows actually moved most of the carcasses to the lake beds.

Mark Norell of the American Museum of Natural History thinks that the carcasses were indeed transferred into lake beds by the eruptions. "At other sites, the bones end up jumbled and scavenged," Norell said. "Instead, these Jehol remains are just exquisitely preserved."

The finding is published in Nature Communications.