Some of these fossils are so complete that researchers can determine what a dinosaur had for breakfast on the day it died. Others include impressions of an animal's muscles and skin, as well as hair, feathers and scales.
The fossils tell us that back in the lower Cretaceous period this land was humid, and dotted with conifer forests and lakes. They also tell us that, occasionally, thousands of animals were killed at once in a mass mortality event that swept them into a common lakebed-turned-graveyard.
In a new study published in the journal Nature Communications, an international team of scientists makes the case that these catastrophic, mass mortality events were pyrocalstic flows from nearby volcanoes -- the same phenomenon that destroyed and preserved the ancient civilization of Pompeii.
Pyroclastic flows, also known as pyroclastic density currents (PDCs), are a lethal mix of gas and fine volcanic ash that can move at speeds of up to 450 mph. When the gas spews from the volacno it can be more than 1,000 degrees Fahrenheit. It is also poisonous.
The research team, led by Baoyu Jiang of Nanjing University in China, provides a few lines of evidence to back up the claim. For example, it cites the pose of the fossilized animals -- backbone extended, limbs flexed (you can see it in the image of the three fossils above). According to the paper, this pose is typical of victims of PDCs and results from the postmortem shortening of tendons and muscles.
The scientists also found evidence of charring on the animals that is similar to what was found on the victims of Pompeii. And because both freshwater and terrestrial animal fossils were found in the same deposits, the researchers believe that land animals caught up in the PDCs' path landed in lakes.
"The volcanic process that killed and preserved these animals should be the same as the process that preserved at Pompeii," Baoyu said in an email to the Los Angeles Times. "However, differing from the extensive preservation of victim remains at Pompeii, most of the preserved Jehol terrestrial animals are those that were transported into lakes and rapidly buried."
She added that the carcasses of animals that weren't swept into lakes had less chance of becoming preserved because of weathering.
Fossils, volcanoes, dinosaurs, fun! Follow me on Twitter for more like this.