Ediacaran Fossils from China Rewrite Timeline of Animal Evolution

An assemblage of more than 700 Ediacaran fossils from the late Ediacaran period indicates that key animal groups – including the earliest relatives of vertebrates – were already diversifying millions of years earlier than long thought.

Reconstruction of the Jiangchuan biota. Image credit: Xiaodong Wang.

The explosion of animal diversification spanning the transition from the Ediacaran to the Cambrian constitutes one of the most important turning points in Earth’s history.

Yet the fossil record offers only a fragmented view of this transformation: Ediacaran communities bear little resemblance to those of the Cambrian, leaving the pivotal moment when major animal groups emerged frustratingly out of reach.

“Our discovery fills a major gap in the early stages of animal diversification,” said Dr Gaorong Li, a researcher at the University of Oxford.

“For the first time, we demonstrate that many complex animals, normally found only in the Cambrian, were present in the Ediacaran, meaning they evolved much earlier than previously demonstrated by fossil evidence.”

In the study, Dr. Li and his colleagues examined more than 700 specimens from a recently discovered fossil site in Yunnan, southwest China.

The fossil assemblage is between 554 and 539 million years old and is part of the Jiangchuan biota.

Unlike most Ediacaran fossil sites, which preserve organisms primarily as impressions on sandstone surfaces, these fossils are preserved as carbonaceous films, a mode of preservation more typical of famous Cambrian sites such as the Burgess Shale in Canada.

“This discovery is extremely exciting because it reveals a transitional community: the strange world of the Ediacaran gives way to the Cambrian, the next period when animals are much easier to place in groups that are alive today,” said Dr Luke Parry of the University of Oxford.

“When we first saw these specimens, it was clear that these were something totally unique and unexpected.”

The assemblage contains the oldest known relatives of deuterostomes, the larger group that today includes vertebrates such as humans and fish.

Also among the specimens are the ancestors of modern sea stars and their closest relatives, the acorn worms (Ambulacraria).

They have a U-shaped body and were attached to the seabed with a stalk, with a pair of tentacles on the head used for catching food.

“The presence of these ambulacrarians during the Ediacaran period is really exciting,” said Dr Frankie Dunn of the University of Oxford.

“We have already found fossils that are distant relatives of sea stars and sea cucumbers and we are looking for more.”

“The discovery of ambulacral fossils in the Jiangchuan biota also means that chordates – animals with a backbone – must also have existed at this time.”

Other ancestral groups among the fossils include bilaterian worm-like animals, some with complex dietary adaptations, as well as rare fossils interpreted as early comb jellies.

Many specimens exhibit novel combinations of anatomical features that do not match any known Ediacaran or Cambrian species.

“Our results indicate that the apparent absence of these complex animal groups at other Ediacaran sites may reflect differences in preservation rather than a true biological absence,” said Dr Ross Anderson of the University of Oxford.

“Carbonaceous compressions like those at Jiangchuan are rare in rocks of this age, meaning similar communities may simply not have been preserved elsewhere.”

The discovery is described in a journal article Science.

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Gaorong Li and others. 2026. The dawn of the Phanerozoic: a transitional fauna from the Late Ediacaran of southwest China. Science 392 (6793): 63-68; doi: 10.1126/science.adu2291