A newly identified fossil site in southwest China is changing scientists’ understanding of how complex animal life first developed on Earth. The discovery shows that many major animal groups were already present before the Cambrian Period began. The research was led by teams from Oxford University’s Museum of Natural History and Department of Earth Sciences, along with Yunnan University in China, and was published on April 2 in Science.
For years, scientists believed that the rapid rise of diverse and complex animals, known as the Cambrian explosion, began around 535 million years ago. This period marked a dramatic shift from simple organisms to a wide variety of more advanced life forms. The new study now indicates that this transformation started at least 4 million years earlier, during 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 Fossils Show Early Animal Diversity
The fossils were uncovered in the Jiangchuan[1] Biota in Yunnan Province, where researchers collected more than 700 specimens dating from 554 to 539 million years ago. This site reveals a rich and varied Ediacaran ecosystem, including previously unknown species as well as animals once thought to appear only later in the Cambrian.
Among the most important findings are fossils believed to be the oldest known relatives of deuterostomes, a major group that includes vertebrates such as humans and fish. These discoveries extend the fossil record of this group back into the Ediacaran Period for the first time.
The collection also includes early relatives of starfish and their close counterparts, the acorn worms (the Ambulacraria[2]). These organisms had U-shaped bodies and were anchored to the seafloor by a stalk. Tentacles near their heads were likely used 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 Creatures and Transitional Ecosystems
Other fossils include worm-like bilaterian animals (having bilateral symmetry), some showing complex feeding strategies, along with rare specimens thought to represent early comb jellies.
Many of the fossils display unusual combinations of features, such as tentacles, stalks, attachment discs, and feeding structures that could be turned inside out. These combinations 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.”
Solving a Long-Standing Evolution Mystery
The findings help answer a long-standing question in evolutionary biology. Previous genetic studies and fossil traces suggested that many animal lineages existed before the Cambrian explosion. However, clear fossil evidence from this earlier period had been largely missing until now.
Exceptional Preservation Reveals Hidden Details
Unlike most Ediacaran fossil sites, which preserve organisms as simple impressions in sandstone, the Jiangchuan Biota fossils are preserved as carbonaceous films. This type of preservation is more commonly associated with famous Cambrian fossil sites such as the Burgess Shale in Canada. It allows scientists to see fine details, including feeding structures, digestive systems, and organs related to movement.
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.”
Years of Fieldwork Lead to Breakthrough Discovery
The fossils were found by a research team at Yunnan University, led by Professor Peiyun Cong and Associate Professor Fan Wei. The group spent nearly a decade searching for diverse Ediacaran animal fossils. Although fossils had previously been discovered in eastern Yunnan, they were limited to algae and did not include 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 research, 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
- Pronounced ‘jing-choo-an.’
- Ambulacraria, from the latin ambulacrum, meaning “a walk planted with trees.”