Fossil site in southwest China fills in critical gap before Cambrian period

Gaorong Li and colleagues have uncovered a new fossil assemblage in the Jiangchuan Biota in Yunnan, Southwest China that fills a critical gap in our knowledge of the transition between the strange, soft-bodied animals of the Ediacaran period and the ancestral forms of almost all modern animal life during the Cambrian period. Little is known about this period of significant geological and biological upheaval, so finding a fossil assemblage from this time (roughly 575-539 million years ago) could provide insight into one of the planet’s most spectacular periods of animal diversification. Li et al. identified more than 700 specimens, including new taxa, preserved as carbonaceous films at the site. Among the specimens are a mix of Ediacaran and Cambrian-like body plans, many with well-preserved eating and locomotion structures. The fossil assemblage contains several bilaterian specimens (animals characterized by bilateral symmetry in their embryonic stage, which dominate modern animal species), suggesting bilaterians may have begun to diversify earlier than suspected.