Oldest Deuterostome Fossil from Jiangchuan Biota Reveals Ancient Roots Across Ediacaran–Cambrian Transition

The Conversation reports on fossils from the Jiangchuan biota in Eastern Yunnan that illuminate the late Ediacaran to early Cambrian transition. Led by Gaorong Li with Oxford colleagues Luke Parry and Frankie Dunn, the team describes a bizarre worm anchored to the seafloor and a diverse fossil community that blends features of Ediacaran organisms with Cambrian animals. Most strikingly, they report the oldest evidence for deuterostomes, the lineage that includes humans, implying our invertebrate relatives share deep roots with early complex life. The findings, published in Science, are summarized here by The Conversation to explain how this discovery reshapes views of animal origins and the Cambrian transition.

Overview

Life on Earth is extraordinarily diverse and capable of colonising nearly every environment, from deep-sea vents to the air above us. The Cambrian explosion around 538 million years ago produced a remarkable variety of animals recognizable to today’s groups, but scientists have long debated whether this burst occurred abruptly or reflected a longer, more gradual process. The Conversation reports new fossil evidence from the Jiangchuan biota in eastern Yunnan, China, that helps address this question by revealing ancient, complex animals alongside enigmatic Ediacaran life. The work, led by Gaorong Li with Luke Parry and Frankie Dunn of Oxford, was published in Science and sheds light on how early animal evolution unfolded across the Ediacaran–Cambrian boundary.

Discovery and Field Work

In spring 2023, Gaorong Li, then a PhD student, identified a strange worm tethered to the seafloor by an anchoring disc within Jiangchuan rocks. This organism, nicknamed the “bugle worm,” possessed a proboscis that could be turned inside out to feed, signaling a complex animal lifestyle not seen in the Ediacaran record alone. The initial description centered on the anchoring disc and, previously, a fragment named Cycliomedusa. Li and colleagues soon realized the entire organism revealed a more complete animal, prompting further rock splitting in 2024 with Oxford collaborators Li and Dunn joining the field program. The Jiangchuan biota yielded fossils with features bridging Ediacaran and Cambrian forms, including a primitive Mackenzia-like animal and ctenophores, alongside burrows and traces that mark the emergence of bilaterian life.

In addition to discovering worms and predatory organisms, the project revealed what appears to be the oldest evidence for deuterostomes, the branch that includes modern vertebrates and their invertebrate relatives. The Jiangchuan assemblage shows that diverse complex life persisted across the boundary rather than a single, rapid turnover at the start of the Cambrian.

Key Findings and Significance

One of the most important outcomes described is the demonstration of deuterostomes in the Jiangchuan biota, dating roughly to 554–539 million years ago. A deuterostome cambroernid fossil is illustrated with a scale bar of 2 mm, and several specimens exhibit stalks and tentacles reminiscent of Cambrian cambroernids. This finding implies that the lineage to which humans belong has deep roots in the Ediacaran period, reshaping our understanding of early animal evolution and suggesting that multiple animal groups coexisted with Ediacarans for millions of years.

Researchers report that some Jiangchuan specimens combine traits previously associated with the Ediacaran world and with Cambrian organisms, including forms related to the Cambrian assays like Mackenzia and other worm-like and swimming predators such as ctenophores. The discovery underscores a more complex early animal landscape, one in which modern invertebrate relatives and strange Ediacaran forms interacted before the classic Cambrian bloom.

As Li and colleagues note, the Jiangchuan biota reveals that our own evolutionary story has roots in the Ediacaran, a finding that supports the idea of an extended, multi-lineage origin for bilaterians rather than a sudden Cambrian event. The team emphasizes that evidence from fossil burrows and trails has hinted at this broader narrative, but the Jiangchuan fossils provide direct glimpses of the animals themselves rather than only traces of their activity.

Quotes

"Animal life is extraordinarily diverse and complex, having colonised almost all environments on Earth – from hostile hydrothermal vents in the deep sea to the skies across our continents." - Luke Parry

"We nicknamed it the 'bugle worm'." - Gaorong Li

"Most striking of all, we found the oldest evidence for the group to which we humans belong: the deuterostomes." - Gaorong Li

"Diverse complex animal life has a more ancient heritage than the Cambrian explosion." - Luke Parry

Implications for Evolution and Paleobiology

Li and coauthors argue that the Jiangchuan biota demonstrates a quiet but persistent diversity of complex life across the Ediacaran–Cambrian transition. Rather than a sharp, singular Cambrian explosion, the data support a protracted period in which deuterostomes and other bilaterian lineages were already developing their distinctive body plans. This expands the timeline for the emergence of key animal groups and emphasizes the role of the Ediacaran biosphere as a more integral part of the tree of animal life than previously recognized. The discovery broadens our view of the origins of modern animal lineages and highlights the value of continued field work in lesser-known fossil assemblages around the world.

In summary, the Jiangchuan biota provides a crucial data point for understanding early animal evolution, showing that humans’ closest invertebrate relatives date back further than once thought and that a mosaic of life persisted well before and during the Cambrian explosion. The interdisciplinary collaboration between Li, Dunn, Parry, and their teams underscores the importance of integrating fieldwork, paleontology, and modern analytical methods to reconstruct deep-time evolutionary histories.