One of the most transformative events in Earth's history was the rapid diversification of animal life, resulting in a dramatic increase in complexity and diversity from simpler life forms.

Up to now, this was thought to have occurred at the start of the Cambrian Period, in an event known as the Cambrian explosion, starting around 535 million years ago. The new study, however, shifts this timeframe back by at least 4 million years, to the end of the Ediacaran period.

Lead author Dr. Gaorong Li (Yunnan University at the time of the study, now Museum of Natural History, Oxford University), said, "Our discovery closes a major gap in the earliest phases of animal diversification. For the first time, we demonstrate that many complex animals, normally only found in the Cambrian, were present in the Ediacaran period, meaning that they evolved much earlier than previously demonstrated by fossil evidence."

The discovery comes from the Jiangchuan Biota in Yunnan Province, southwest China, where more than 700 fossil specimens were recovered, aged between 554 and 539 million years old. The fossil site revealed a diverse community of Ediacaran organisms—both new, undescribed animal forms and groups known from the Cambrian period.

Most strikingly, the international team identified fossils thought to be the oldest known relatives of deuterostomes—the broader group that today includes vertebrates such as humans and fish. The new fossils push the fossil record of deuterostomes back into the Ediacaran Period for the first time.