A fossil site in Yunnan province, China, has yielded over 700 specimens dating from 554 to 537 million years ago, challenging the notion of a sudden diversification of complex life during the Cambrian explosion. The Jiangchuan biota includes bilaterians, deuterostomes, and previously unknown forms from the Ediacaran period. Researchers say these findings indicate animal communities had foundations before the Cambrian.
Palaeontologists led by Gaorong Li at Yunnan University in Kunming discovered the Jiangchuan biota, a rich fossil bed contradicting the idea that complex life emerged abruptly around 541 million years ago. The site preserves animals with bilateral symmetry, including two new deuterostome species—a group encompassing vertebrates—that were already diverse in the late Ediacaran, 554 to 537 million years ago. Li, who began excavating in mid-2022 expecting only algae, found cambroernids with coiled bodies and tentacles, previously unknown before the Cambrian, as well as forms resembling the Cambrian organism Margaretia, described as tube-like structures with holes like ventilation pipes. The most common fossils depict animals anchored to the seafloor with extendable tubular appendages, evoking the sandworm from Dune, and mobile sausage-shaped worms with mouths, guts, and pharynxes akin to modern animals but in unfamiliar combinations, Li said. Ross Anderson at the University of Oxford, part of the team, noted that the fossils reveal a more complex picture of animal diversity's origins, suggesting the Cambrian explosion may have been a slower process. Joe Moysiuk at Manitoba Museum emphasized that while preservation lacks fine details, the finds provide better timing for animal body plan divergence over about 30 million years across the Ediacaran-Cambrian boundary, without invalidating the explosion itself. Han Zeng at the Chinese Academy of Sciences called it a potential breakthrough if verified, urging further study on similar Precambrian fossils in South China. The research appears in Science (DOI: 10.1126/science.adu2291).