The fossil bed has the remains of dinosaurs, birds, mammals, lizards and plants from 120 million years ago in the Early Cretaceous. It is possible that the volcanic flow, composed of superheated gas and debris, cooked everything in its path, but at the same time buried and preserved the remains in the volcanic dust.
The report was led by Baoyu Jiang of Nanjing University and has been published in Nature Communications. The collection of fossils, called Jehol Biota, was first excavated nearly a century ago, but only in the last few decades has the marvel of this place been revealed.
Many of the fossils have retained features like feathers, stomach contents, hair and skin, providing archaeologists with valuable snapshot of life in that period. The hot ash and high temperatures seem to have created a mold around these animals and many of them also displayed bent limbs -- a key indicator of pyroclastic volcanic flows.
"All the evidence supports this hypothesis," said study co-author Jin Meng, a paleontologist at the American Museum of Natural History in New York. "Many or most of the vertebrate fossils were preserved this way."
But some question whether a pyroclastic flow could have preserved these animals and dinosaurs. Patrick Orr, a geologist at the University College Dublin, says he is "intrigued" by how these fossils stayed together and did not disintegrate in the extreme heat.
"I'm not saying the authors are incorrect," he said, "but there are other plausible mechanisms (for such fossil preservation) that have been reported elsewhere. … Like all good, provocative papers, this challenges existing ideas and sets up a whole new set of questions."
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