A Cretaceous Pompeii
In the rolling hills of China's Liaoning province lies a fossil site of extraordinary scientific value. Known as the Jehol Biota, these fossil beds contain the remains of an entire ecosystem that thrived between 133 and 120 million years ago, during the Early Cretaceous period. The fossils are found within the Yixian and the slightly younger Jiufotang geological formations. These layers are made of fine-grained, laminated shales mixed with volcanic ash.
The reason for the stunning preservation is geological. The region was a dynamic region of lakes and active volcanoes. Intermittent eruptions blanketed the area in fine ash, which settled at the bottom of the lakes. This ash rapidly buried fish, plants, insects, and terrestrial animals that were washed into the water. The fine sediment and low-oxygen conditions at the lake bottom prevented scavenging and slowed decay, preserving skeletons in articulation and, remarkably, capturing soft tissues like skin, hair, and feathers. This has earned the site the nickname "China's Dinosaur Pompeii".
Dinosaurs in living color
The most famous fossils from the Jehol Biota are the feathered dinosaurs. The first non-avian dinosaur found with evidence of feathers, Sinosauropteryx, was discovered here in 1996. Its body was covered in simple, filament-like feathers. Even more impressive is the preservation of microscopic pigment-containing organelles called melanosomes within the fossilized feathers.
By studying these structures with scanning electron microscopes, scientists can determine the actual colors of these animals. Melanosomes come in different shapes that correspond to different pigments. Sausage-shaped eumelanosomes produce black and grey colors, while spherical phaeomelanosomes create reddish-brown and yellow tones.
Analysis of Sinosauropteryx revealed it had a reddish-brown back and a light-colored belly. This pattern, called countershading, is a common form of camouflage in modern animals. Its long tail had alternating rings of reddish-brown and white. The dinosaur also had a dark, raccoon-like "bandit mask" across its eyes. Other dinosaurs from the beds show different color patterns. The four-winged dinosaur Microraptor was covered in black and glossy feathers. The specific layered arrangement of its melanosomes indicates the feathers were iridescent, shimmering with a blueish sheen like a modern crow or grackle.