February 5, 2014
Volcanic Activity Led To Demise Of Chinese Dinosaurs: Study
[ Watch the Video: Pyroclastic Eruptions Preserved Fossil Beds In China ]
April Flowers for redOrbit.com - Your Universe OnlineThe exceptional preservation and diversity of dinosaur, bird and early mammal fossils present in the fossil beds of northern China are famous. How these creatures died, and why hundreds of creatures from different habitats were buried together on ancient lake floors, has yet to be understood.
A new study, published in Nature Communications, claims that the animals were likely killed by a series of volcanic eruptions more than 120 million years ago. Much like Pompeii, the ash entombed and preserved them.
National Geographic reports that Baoyu Jiang, of China's Nanjing University, worked with a team to analyze fossils and sediment. They concluded that lethal, sudden pyroclastic volcanic eruptions marked by air blasts, hot gas, and ground-hogging clouds of fine ash likely smothered, charred, and then carried forward everything in their path to create these bone beds. These events would explain why so many creatures came to be buried on lake floors, and how they remained well preserved enough that they retain signs of soft tissue, such as feathers, tens of millions of years later.
Paleontologists have suspected that volcanic eruptions had some part in the creation of China's Jehol fossils for a long time. Jiang says that everything about the fossils is explained by the eruptions, which "not only caused major casualties as they [do] today, but also transported some of the remains into nearby lakes and rapidly buried the remains."
The study findings compare the charred bones in the study to ones found in the ruins of Pompeii when Mount Vesuvius exploded in 79 AD. The team also analyzed ashy sediments collected from across the region to explain the preservation and accumulation of the fossils.
"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," says paleontologist Michael Benton, of the U.K.'s University of Bristol, by email. "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," he adds.
Approximately 120 to 130 million years ago, the eruptions occurred across northern China. The team collected and analyzed the ash encasing 14 well-preserved fossils from five bone beds. The 14 fossils include the crow-size bird Confuciusornis and the parrot-faced dinosaur Psittacosaurus.
The ashes covering the charred bone are fine-grained, similar to pyroclastic ash seen in the massive 1883 eruption of the Indonesian volcano Krakatoa. The research team said that the death poses of the Chinese fossils resemble those of other pyroclastic ash victims, with their limbs extended. Spiderweb cracks, like those found on the charred bones of Pompeii victims, were found on the Chinese fossils.
The 10-million-year period of eruptions would have caught birds in the blasts, suffocating them and forcing them from the sky. "The eruptions must have been numerous and caused multiple mass mortalities of both terrestrial and aquatic animals," the study says. The team says that "rather than the mud coating that the bones would have if they floated into lake beds, the fine ash covering appears uniform."
"All of the evidence certainly points to this explanation," says paleontologist Mark Norell, of the American Museum of Natural History in New York, who was not part of the study. "Looking at the exceptional preservation and the numbers [of fossils], it just seems a noxious gas cloud swept in and took them all out."
Benton is cautious about fully embracing this new explanation for how the creatures ended up in the fossil beds. He thinks the findings are "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 says. "At Pompeii, people were overwhelmed and killed, but not transported."
Norell is more convinced by the new theory. He says that the idea of volcanic air blasts pushing remains into lake beds has been a topic of consideration for paleontologists for years.
"At other sites, the bones end up jumbled and scavenged," Norell says. "Instead, these Jehol remains are just exquisitely preserved."
"This really is a dinosaur version of Pompeii, 125 million years old," says paleontologist Stephen Brusatte of Scotland's University of Edinburgh, who was not part of the study. "These volcanoes were agents of death, but also a godsend when it came to fossil preservation."
Brusatte adds, "Without such an unusual preservational setting, we would never get so many well-preserved fossils with details of skin, muscles, feathers, and other soft tissues. There's a reason these types of fossils are rare—because it takes extraordinary events like mega volcanic eruptions to preserve them."
Norell adds that the volcanic findings might also help point the way to finding future fossil beds across Mongolia and northern China and perhaps pointing to additional once-volcanic sites to investigate for dinosaur bones.
"I think there is a lot of work left for us in finding fossils in China," he says.