A treasure trove of fossilised dinosaurs and other long-extinct species in Liaoning province was created, Pompeii-style, by an erupting volcano, scientists have said.
A seam of rock known as the Yixian and Jiufotang formations is the burial ground of an astonishing array of creatures that lived about 120 million years ago in the Early Cretaceous period.
Called the Jehol Biota, it is the richest and widest source of fossils found and has been the focus of study since the late 1950s.
It has yielded the remains of dinosaurs, pterosaurs, early birds and mammals, as well as turtles, lizards, freshwater fish, frogs, plants and insects, which inhabited a long-gone area of lakes and conifer forests.
Many of the specimens are astonishingly well preserved, revealing even scales, feathers, hair or skin.
The secret of the preservation, according to a study led by Jiang Baoyu of Nanjing University in Jiangsu province, lies in a volcanic explosion that extinguished life and then buried it in dust, locking it away for eternity.
Jiang's team looked at 14 bird and dinosaur fossils and the thin layer of darkish sediment in which they were found at five locations.
The big killer, they believe, was pyroclastic flow - a vicious outpouring of hot, suffocating volcanic gas and superfine dust, moving at gale-force speed. Under the microscope, debris from plants showed blackened carbon streaks and in the fossilised skeletons hollow bones were filled with fine quartz grains.
But the biggest indicator of all came from criss-crossed cracks at the bone edges, caused by heat stress.
This phenomenon was also found in the bones of victims at Pompeii, the Roman town that was buried by an eruption of Vesuvius in 79 AD, the authors said in a paper, published in the journal Nature Communications .
Previous researchers had noted the Jehol Biota sediment was volcanic.
They surmised that there had been a mass die-out as so many different species - terrestrial, aquatic and bird - were all clustered in one area.
But suspicions an eruption was to blame lacked hard evidence until now.
The dust flow from the volcano swept many dead creatures into lake beds where they were immediately buried in oxygen-starved conditions, according to the new study.
"Terrestrial vertebrate carcasses transported by and sealed within the pyroclastic flows were clearly preserved as exceptional fossils through this process," the researchers said.