A goldmine of fossils found in northern China is believed to hold the remains of early creatures that died in volcanic eruption 120 million years ago.
The fossils were believed to have been transported by the molten rock into lakebeds, which turned out to be their final resting place. A volcanic eruption would explain how they remained so well preserved, National Geographic reported.
"That's quite a radical, new idea," Mike Benton , a paleontologist at the University of Bristol told NBC. In the past researchers had believed the animals had been carried to the river beds by running water.
The event was compared to the tragic eruption of Mt. Vesuvius Pompeii that killed scores of Italians in 79 A.D., National Geographic reported.
The team looked at the "ashy sediment" to further determine how the fossils were preserved.
"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," Benton told 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."
The researchers also found "re-crystallized" bone fossils, suggesting they had been exposed to extreme hot at one point, NBC reported. Fish fossils have been found in the region, but only land animals such as mammals and dinosaurs showed signs of transport.
Birds may have "suffocated and fell from the sky," National Geographic reported.
"The eruptions must have been numerous and caused multiple mass mortalities of both terrestrial and aquatic animals," the study said, National Geographic reported.
"All of the evidence certainly points to this explanation," paleontologist Mark Norell of the American Museum of Natural History in New York, who was not part of the study, told National Geographic. "Looking at the exceptional preservation and the numbers [of fossils], it just seems a noxious gas cloud swept in and took them all out."