An Explosion in Stone
The Chengjiang Fossil Site, a UNESCO World Heritage location in Yunnan province, records life on Earth 518 million years ago. The fossils are found within a geological layer known as the Maotianshan Shales, which were once the muddy floor of a shallow tropical sea. This site documents the Cambrian Explosion, a geologically brief period when almost all major animal groups first appeared in the fossil record. The Chengjiang Biota is 10 million years older than the famous Burgess Shale in Canada and contains a wider variety of species.
The exceptional preservation is the result of sudden mudslides that rapidly buried entire marine communities. This quick burial in fine-grained sediment created an oxygen-poor environment, halting decay and preserving soft tissues in great detail. This type of fossil deposit is known as a Lagerstätte. The fossils record a complete marine ecosystem, with evidence of complex food webs topped by large predators. Over 280 species have been identified, with at least 16 animal phyla represented.
The Creatures of Chengjiang
Among the most significant finds at Chengjiang are the earliest known vertebrates. Creatures like Myllokunmingia and Yunnanozoon, small, fish-like animals just a few centimeters long, show evidence of skulls, fins, and other vertebrate features, pushing back the known origin of our own distant ancestors.
The ecosystem's apex predator was Anomalocaris, a large, swimming arthropod relative that could reach up to a meter in length. Its formidable, spiny grasping appendages and circular mouth made it a fearsome hunter. Other inhabitants included the bizarre Hallucigenia, arthropods like trilobites, and Fuxianhuia protensa, a creature that provided a discovery. In 2012, paleontologists identified the fossilized brain and optic nerves of a Fuxianhuia specimen. This 520-million-year-old nervous system—the oldest ever found, revealed a complex three-part brain structure similar to that of modern insects and crustaceans, showing that complex brains evolved very early in animal history.