Dinosaurs found frozen mid-sleep after prehistoric ash burial similar to Pompeii

Imagine a lush prehistoric forest in what is now northern China, full of feathered dinosaurs, early birds, and tiny mammals going about their daily lives, and then, suddenly, a nearby volcano erupts and entombs them all alive. That’s not science fiction. It actually happened about 120 million years ago. And now scientists have finally figured out how.

Some of the most jaw-dropping fossils ever found are in a mass grave in the bed of a Chinese lake, creatures frozen in their death poses so precisely that scientists can still see feathers, fur and soft tissue. Scientists were baffled for years about what killed them all at once. Now, a study in Nature Communications has come up with an answer, and it’s as dramatic as it sounds.

They didn't just get buried, they got fried
The fossils are from what scientists call the Jehol Biota, an ancient ecosystem that flourished in what is now northern China during the early Cretaceous period. Imagine dinosaurs alongside the first birds and mammals, amidst conifer forests and volcanic mountains. The fossils were encased in the Yixian and Jiufotang formations of rock beds rich in volcanic stuff.

According to a 2014 study published in Nature Communications, researchers examined both the fossils and the chemistry of the surrounding rock and sediment and concluded that the animals were killed by pyroclastic density currents, or fast-moving flows of superheated ash and gas that blast out of an erupting volcano. These are just a few of the most lethal forces a volcano can unleash.

The animals were pretty much "put in the grill," said George Harlow, a mineralogist at the American Museum of Natural History and co-author of the study. The bones exhibited black streaks consistent with charring, clear evidence of extreme heat being involved.

Think Pompeii, but with dinosaurs
If you’ve seen photos of Pompeii, you’re familiar with the image: people frozen in their final moments, preserved in volcanic ash for almost 2,000 years. These Chinese animals went through the same basic thing, just 120 million years before.

The victims of Pompeii faced something very similar. Based on Mastrolorenzo et al. (2010) in PLOS ONE, the exposure to pyroclastic surges of at least 250°C was enough to cause instant death, even to those sheltered inside buildings. The heat was the main killer, not suffocation by ash as once thought. The Jehol animals probably had the same fate, just on a much older timeline.

Scientists ruled out other explanations
Some researchers had previously suggested the Jehol fossils may have floated into the lake naturally or been washed there by flooding. That died in the new study. The structure of the sediment layers and the fact that so many skeletons were found perfectly intact did not match a gradual burial by water. Floods carry bodies away, in a jumble and a spray. These animals were exactly where the catastrophe had placed them.

Why it matters to us now
Pyroclastic flows are not a thing of the past. Such deadly currents were created by Krakatoa, Mount St. Helens, and the 1902 eruption of Mount Pelée in Martinique, which killed some 30,000 people.

Scientists are studying how these events preserve biological material to recreate ecosystems that existed long before humans arrived. The Jehol fossils have already changed our perception of feather evolution and the development of flight in early birds.

In a way, these Chinese dinosaurs are doing for paleontology what Pompeii has done for archaeology, offering a freeze-frame of a living world that would otherwise be lost forever.