Scientists Just Rewrote the Timeline of Complex Life on Earth

Scientists have discovered fossils showing that complex animals existed millions of years before the Cambrian explosion, reshaping the timeline of life on Earth.

The finds reveal a strange, diverse ecosystem where early versions of modern animals were already evolving.

Ancient Fossil Discovery Rewrites the Timeline of Complex Life

A newly identified fossil site in southwest China is reshaping scientists’ understanding of how complex animal life first emerged on Earth. The discovery shows that many major animal groups had already evolved before the Cambrian Period began. The research, led by scientists from Oxford University’s Museum of Natural History and Department of Earth Sciences along with Yunnan University in China, was published today (April 2) in Science.

For decades, scientists believed that the rapid rise in animal diversity and complexity, known as the Cambrian explosion, began around 535 million years ago. This event marked a turning point when simple organisms gave way to more complex forms. However, the new findings push that timeline back by at least 4 million years, placing the emergence of many complex animals in the late 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.”

Jiangchuan Biota Reveals Early Animal Diversity

The fossils come from the Jiangchuan^[1] Biota in Yunnan Province, where researchers uncovered more than 700 specimens dating from 554 to 539 million years ago. The site contains a rich mix of Ediacaran life, including entirely new species as well as organisms previously thought to appear only in the Cambrian.

One of the most important discoveries is evidence of early deuterostomes, a major group that includes modern vertebrates such as humans and fish. These fossils represent the oldest known relatives of this group, extending their fossil record back into the Ediacaran Period for the first time.

Among the specimens are early relatives of starfish and their close kin, the acorn worms (the Ambulacraria^[2]). These creatures had U-shaped bodies and were anchored to the seafloor by a stalk. They used tentacles near their heads to capture food.

Co-author Dr. Frankie Dunn (Museum of Natural History, Oxford University) said: “The presence of these ambulacrarians in the Ediacaran period is really exciting. We have already found fossils which are distant relatives of starfish and sea cucumbers and are looking for more. The discovery of ambulacrarian fossils in the Jiangchuan biota also means that the chordates – animals with a backbone – must also have existed at this time.”

Strange Early Creatures and Transitional Life Forms

The fossil collection also includes worm-like bilaterian animals (having bilateral symmetry), some showing advanced feeding adaptations, along with rare specimens interpreted as early comb jellies.

Many of the fossils display unusual combinations of features, including tentacles, stalks, attachment discs, and feeding structures that could be turned inside out. These forms do not match any known species from either the Ediacaran or Cambrian periods. “For instance, one specimen looks a lot like the sand worm from Dune!” Dr. Dunn added.

Co-author Associate Professor Luke Parry (Department of Earth Sciences, Oxford University) added: “This discovery is extremely exciting because it reveals a transitional community: the weird world of the Ediacaran giving way to the Cambrian, the following time period where the animals are much easier to place in groups that are alive today. When we first saw these specimens, it was clear that this was something totally unique and unexpected.”

Filling a Major Gap in Evolutionary History

These findings help resolve a long-standing mystery in evolutionary biology. Genetic studies and trace fossils have suggested for years that major animal groups evolved before the Cambrian explosion. However, clear fossil evidence of these animals had been largely missing from Ediacaran rocks until now.

Exceptional Fossil Preservation Reveals Hidden Details

Most Ediacaran fossil sites preserve organisms as simple impressions in sandstone. In contrast, the Jiangchuan Biota fossils are preserved as carbonaceous films, a type of preservation more commonly seen in famous Cambrian sites such as the Burgess Shale in Canada. This rare preservation allows scientists to observe fine anatomical details, including feeding structures, digestive systems, and movement-related features.

Co-author Associate Professor Ross Anderson (Museum of Natural History, Oxford University) said: “Our results indicate that the apparent absence of these complex animal groups from other Ediacaran sites may reflect differences in preservation rather than true biological absence. Carbonaceous compressions like those at Jiangchuan are rare in rocks of this age, meaning that similar communities may simply not have been preserved elsewhere.”

A Decade of Fieldwork Leads to Breakthrough

The fossils were discovered by a Yunnan University research team led by Professor Peiyun Cong and Associate Professor Fan Wei, who spent nearly ten years searching for diverse Ediacaran animal fossils. Although the rocks in eastern Yunnan were known to contain fossils, earlier discoveries had only revealed algae rather than animal remains.

Associate Professor Fan said, “After years of fieldwork, we finally found several sites with the right conditions where animal fossils are preserved together with the abundant algae.”

Professor Feng Tang from the Chinese Academy of Geological Science, Beijing, whose earlier work helped guide the team’s efforts, said: “The new fossils provide the most compelling evidence for the presence of diverse bilaterian animals at the end of the Ediacaran, evidence people have searched for across decades.”

Notes

1. Pronounced ‘jing-choo-an.’
2. Ambulacraria, from the latin ambulacrum, meaning “a walk planted with trees.”

Reference: “The dawn of the Phanerozoic: a transitional fauna from the late Ediacaran of Southwest China” 2 April 2026, Science.
DOI: 10.1126/science.adu2291

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