Huge Volcanic Eruptions Preserve Dinosaur Fossils for 120 Million Years

Northern China is home to fossils that are famously diverse and well preserved, but for unknown reasons. Now, researchers think volcanic eruptions that took place more than 120 million years ago entombed and preserved the animals, in a similar way to the victims of Pompeii.

In a study published in Nature Communications, Baoyu Jiang of China's Nanjing University concluded that a pyroclastic flow - a fast moving current of gas and rock - issuing from a series of volcanic eruptions likely suffocated and then encased any animals on the ground or in the air close to the volcanoes.

Working with a team, Jiang compared the charred fossils from Jehol, China with remains from the Roman victims of the 79 A.D. eruption of Mount Vesuvius.

"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."

Examining the encasing of fossils from five bone beds, the team found the ash similar to pyroclastic matter seen in other massive volcanic eruptions. Excavators unearthed carcasses with their limbs extended and spiderweb cracks in their bones, consistent with the victims of Pompeii and other pyroclastic ash eruptions, according to the study.

However, Benton said he believes the study's assertion that the animals were transported to the fossil beds is "unlikely." "I think the basis of the work is good, but the evidence that the pyroclastic flows actually transported the carcasses in most cases seems unlikely," Benton told National Geographic. "At Pompeii, people were overwhelmed and killed, but not transported."

Mark Norell of the American Museum of Natural History in New York told National Geographic that he was convinced the carcasses were pushed 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 results of this study will point other researchers to the sites of erupted volcanoes in hopes of finding more collections of well preserved dinosaur remains, Norell added.