A deuterostome cambroernid fossil from the Jiangchuan Biota (~554-539 million years old) and artist's reconstruction, scale bar: 2mm. Credit: Gaorong Li & Xiaodong Wang.

A newly discovered fossil site in southwest China has transformed our understanding of how complex animal life emerged on Earth, revealing that many key animal groups had already evolved before the start of the Cambrian Period. The study, led by researchers at Oxford University's Museum of Natural History and Department of Earth Sciences as well as Yunnan University in China, has been published in Science.

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.

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Reconstruction of Jiangchuan biota (~554-539 million years ago). Credit: Xiaodong Wang.

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.

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