JUANA SUMMERS, HOST:
In northeast China, there's a place that's offered up a treasure trove of exquisite dinosaur fossils over the years. The prevailing theory says they were preserved suddenly by volcanic activity. But science reporter Ari Daniel says new research suggests an alternative explanation, one that is much less catastrophic.
ARI DANIEL, BYLINE: A few hundred miles northeast of Beijing is a geological formation dating back to the early Cretaceous.
PAUL OLSEN: It's produced the majority of the spectacular feathered dinosaurs of China.
DANIEL: These flattened fossils are incredibly well preserved, says Paul Olsen, an Earth scientist at Columbia University. There's also a whole suite of 3D fossils.
OLSEN: They're astoundingly complete, down to the very, very last bone. And they're often in positions that look like they were just frozen in an instant.
DANIEL: Olsen says it's this appearance combined with the deposits being rich in volcanic ash that's led many researchers to conclude...
OLSEN: That the animals were catastrophically entombed by either volcanic mud flows or killed by volcanic ash or some sort of major catastrophe.
DANIEL: But Olsen had his suspicions. He reflected on the people who died in Pompeii when Mount Vesuvius erupted and quickly buried the city.
OLSEN: They are in really contorted positions that tell you they were in extreme discomfort when they died.
DANIEL: But many of the dinosaur fossils unearthed in this part of China look like they're sleeping peacefully, no visible signs of discomfort from fiery volcanic activity. Paleontologists have also found clutches of baby dinosaurs clustered together.
OLSEN: How would those animals ever stay together if they were enveloped in a massive flowing mass of material? It's not a mystery what happens to organisms when they get caught up in these things. They get ripped to shreds.
DANIEL: Olsen and his colleague studied two of those 3D dinosaur fossils. They compared the sediments inside and outside the skeletons.
OLSEN: The sediment inside the animal in both dinosaurs was much finer grained than the sediment outside of it.
DANIEL: Which indicated to Olsen that the animals were buried with their skin and muscles still intact. So he suggests an alternative explanation for how these dinosaurs may have died. Their burrows, he says, suddenly collapsed, suffocating them.
OLSEN: Maybe some of them collapsed because a big sauropod dinosaur walked by. Maybe the water-logged mud simply collapsed.
DANIEL: Olsen argues that other animals were likely entombed in sediments at the bottom of a series of deep lakes - no volcanic activity required there either - all taking place over tens of thousands of years. This research is published in the journal PNAS. But paleontologist Baoyu Jiang finds the results unconvincing and speculative.
BAOYU JIANG: The paper is good. But they only analyzed two dinosaur fossils. They even didn't study the fossil in the lake.
DANIEL: Jiang is at Nanjing University in China.
JIANG: Sometimes you find fossils in normal sediment like they found. But most of the time, the feather dinosaur they were preserved closely associated with volcanic ashes. There are many kinds of possibilities.
DANIEL: For Paul Olsen, the takeaway is straightforward, that researchers should be careful to invoke a catastrophic explanation when a simple, more mundane one may well suffice.
OLSEN: In no way does this diminish these fantastic fossils. In fact, for me, it makes them even more marvelous that we get this deep view of diversity so many millions of years ago.
DANIEL: A view made visible by something perhaps rather ordinary.
For NPR News, I'm Ari Daniel.
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