A remarkable fossil discovery in southwestern China is challenging long-held assumptions about when complex animal life first evolved. While the Cambrian explosion, beginning around 539 million years ago, has traditionally been viewed as the moment when most major animal groups rapidly appeared, the newly uncovered Jiangchuan Biota suggests that many of these complex traits were already emerging several million years earlier, during the late Ediacaran period. The site contains more than 700 specimens, including worm-like bilateral animals, early comb jellies, and primitive relatives of starfish and sea cucumbers, as well as unfamiliar forms that do not resemble any known organisms.
These fossils were preserved as carbonaceous films, capturing soft-tissue details such as guts and mouthparts, features rarely preserved. This unusual preservation may explain why such complexity has not been widely observed in earlier fossil records. Rather than a sudden evolutionary burst, the findings suggest a more gradual buildup to the Cambrian explosion, with complex ecosystems already taking shape beforehand but largely hidden due to gaps in fossil preservation.