Researchers Describe "Animal Pompeii"

This "Animal Pompeii" is the result of lethal volcanic flows, according to new work by an international team of geologists and paleontologists, including Museum Curators Jin Meng and George Harlow. The finding helps unravel the mystery behind the preservation history of the Jehol Biota—an ancient ecosystem that existed between 130 to 120 million years ago. The research is published today in Nature Communications.

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. 
Nanjing University/Baoyu Jiang

 “Excavation work in this area has uncovered exquisitely preserved specimens ranging from plants and insects to fishes and non-avian dinosaurs,” said Jin Meng, a curator in the American Museum of Natural History’s Division of Paleontology and an author on the paper. “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.”

The Jehol Biota is preserved in the Yixian and Juifotang rock formations in what was once a landscape of lakes and conifer forests, surrounded by volcanoes. Although scientists have long predicted that volcanism played a role in shaping the remarkable fossils there, the cause of the mass mortalities and preservation history was a mystery. 

Meng, along with George Harlow, a curator in the Museum’s Department of Earth and Planetary Sciences, Baoyu Jiang, a former postdoctoral fellow at the Museum and researcher at Nanjing University, and colleagues at Los Alamos National Laboratory and the Chinese Academy of Sciences, collected samples from fossil birds and dinosaurs from several locations and analyzed them and the sediments in which they were preserved.

Using scanning electron microscopy, x-ray diffraction, and computed tomography (CT) at the Museum, the team found that each of the skeletons had been directly embedded within pyroclastic flows, incredibly fast-moving currents of hot gas and rock that accompany some explosive volcanic eruptions.

Backscattered scanning electron microscope images show charcoalified soft tissues (dark materials) on the Jehol terrestrial vertebrate skeletal fossils (a-b, Psittacosaurus, a ceratopsian dinosaur; c-d, Confuciusornis, a primitive crow-sized bird). 
Nanjing University/Baoyu Jiang

Although the preservation of organisms during volcanic eruptions may differ, the Jehol vertebrates examined in the study were characterized by entombment poses and showed evidence of charring, similar to those associated with victims in Pompeii and Herculaneum, Italy, who were killed during the 79 AD eruption of Mount Vesuvius. The findings suggest that pyroclastic flows led to the mass mortality, entombment, transportation, and ultimate preservation of the Jehol Biota.

Photomicrographs of thin sections show asymmetric and wavy abrasive pits, missing bone material (arrows) and cracks at both upper and lower bone edges, and decreasing modification of bone microstructures of two Jehol terrestrial vertebrate skeletal fossils (a, Psittacosaurus, a ceratopsian dinosaur; b, Confuciusornis, a primitive crow-sized bird). 
Nanjing University/Baoyu Jiang

 “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,” Harlow said. “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.”