518 million year old Chinese fossil rewrites the origin story of starfish

An international team led by Northwest University in Xi'an, China, and the University of Cambridge has described four 518-million-year-old fossils of a new species, Yujingia glutenotunica, from the Maotianshan Shales in Yunnan Province, China. The discovery, published in Current Biology on September 16, 2026, identifies the animal as the closest fossil yet found to the last common ancestor of ambulacrarians, the group that today includes starfish, sea stars, sea urchins and acorn worms.

Ambulacraria is one of the two major branches of deuterostome animals, a classification that dates back to the 1880s. It contains echinoderms, such as starfish and sea urchins, and hemichordates, such as acorn worms. These groups have strikingly different body forms: starfish display fivefold radial symmetry, while acorn worms have bilaterally symmetrical, wormlike bodies. Fossil evidence of their shared origins has been scarce, leaving a gap in the story of how this familiar animal group evolved.

For decades, biologists pictured the ancestor of starfish, sea urchins and acorn worms as a wormlike animal that burrowed into mud and filtered food through its throat, or pharynx, much like a modern acorn worm. The new fossils challenge that view with direct anatomical evidence. Instead of a burrowing filter feeder, Yujingia appears to have been a tentacle-feeding animal that lived on the seabed, capturing organic particles from the water with feathery arms.

The fossils come from the Chengjiang Biota, part of the Maotianshan Shales in Yunnan, a Lagerstatte, or sedimentary deposit, where mud buried animals fast enough to preserve soft tissue. The site dates to roughly 518 million years ago, during the Cambrian explosion, when most major animal groups first appear in the fossil record. The four specimens are among the few ambulacrarian fossils known from before the appearance of mineralized skeletons.

Key Facts

The University of Cambridge reported on September 16, 2026, that the Yujingia fossils measure 8 to 22 millimetres long and preserve the body, gut and appendages. China Daily reported on September 18, 2026, that the specimens range from 8.5 millimetres to 22 millimetres in length and were found near Kunming, Yunnan. The four fossils are rare examples of ambulacrarians without a mineralised skeleton, meaning their soft parts survived only because of exceptional burial conditions.

Yujingia had two distinct sets of appendages. One set was made of featherlike feeding tentacles that captured organic particles from the water. The other set, located lower on the body, is thought to have temporarily anchored the animal to the seabed, though it was likely capable of some movement. Lead author Kaiyue He, from Northwest University in China, said the animal has an elongated, bottlelike form with tentacles spreading above a rounded lower body. Its outline resembles the ritual vase, or yujingping, which inspired the genus name, while its soft, gelatinous membrane inspired the species name. The study was led by Han Jian and He Kaiyue from Northwest University's Department of Geology.

Earth.com reported on September 19, 2026, that the crown of the animal holds two kinds of appendage: six feathery arms, each carrying a row of small side branches with a groove running down the middle that moves food to the mouth, plus slim smooth strips spreading lower down. The team scanned a living feather star, a relative of starfish, and found the arms built alike. The specimens each have a smooth, curved lower body with a dark mass interpreted as the gut and nearby organs. The Chinese name for the species is Jiaomo Yujingchong.

To place Yujingia in the tree of life, the team assembled a dataset of 505 morphological characters across 100 living and extinct taxa and ran a Bayesian phylogenetic reconstruction. The analysis placed Yujingia closer to the last common ancestor of living ambulacrarians than any previously described fossil, with a 91 percent probability that it sits just outside the living ambulacrarians. The results were published in Current Biology on September 16, 2026, with the DOI 10.1016/j.cub.2026.08.053.

Phys.org reported on September 19, 2026, that scientists discovered several 518-million-year-old fossils that reshape understanding of the origins of the animal group containing starfish, showing these animals ate using tentacles rather than passively using gills. Co-author Dr Giovanni Mussini, from Cambridge's Department of Earth Sciences, said the longstanding view was that the ambulacrarian ancestor was a wormlike burrower filtering food through its pharynx, but the new fossil instead suggests it fed with tentacles and was more like starfish and their relatives.

Analysis

What this really means is that the ancestral ambulacrarian was not a pharyngeal filter feeder but a tentacle feeder. The distinction matters because it reverses a widely taught assumption about the deepest branches of deuterostome evolution. Han Jian noted that tentacle-based and pharyngeal filter-feeding evolved independently in separate evolutionary branches, which means the modern acorn worm's feeding style is not a retained ancestral trait but a later specialization. The fossil evidence from Yujingia supports this interpretation directly, rather than relying only on comparisons among living animals.

The fossil also helps explain a long-standing anatomical puzzle. Mussini said the fivefold radial symmetry of starfish and the bilaterally symmetrical, wormlike bodies of acorn worms has been a bit of a mystery until now. Yujingia offers a possible bridge: it had a bilaterally symmetrical body like ours, according to Mussini, but also feathery tentacles more reminiscent of modern sea lilies. That combination of traits suggests the ambulacrarian ancestor was a small, tentaculate animal with a body plan that could later give rise to both the radial echinoderms and the wormlike hemichordates.

The bigger picture here is that the origin of the starfish body plan was not a slow transformation from a burrowing worm into a radial animal, but a direct inheritance from a tentacle-feeding ancestor that already lived on the seabed. Earth.com reported that the combination of alternating pinnules and a ciliated groove is unknown among other early ambulacrarians but occurs in modern sea lilies and some tiny tentaculate worms called pterobranchs. That detail strengthens the case that Yujingia sits near the split between the two great ambulacrarian branches, and it gives researchers a new anatomical reference point for interpreting other Cambrian fossils.

At the same time, the analysis rests on four specimens and a phylogenetic reconstruction based on morphology alone. The 91 percent probability that Yujingia sits just outside living ambulacrarians is strong but not absolute, and soft-bodied fossils always leave room for differing interpretations of preserved features. The second set of appendages, interpreted as an anchoring device, is especially difficult to reconstruct from flattened specimens. Future discoveries from the Chengjiang Biota or other Lagerstatten could test whether the tentacle-feeding model holds across a wider sample.

Why It Matters

The discovery rewrites the origin story of starfish, sea urchins and acorn worms, a group that includes some of the most familiar marine animals. It also clarifies the origins of feeding modes among ambulacrarians, as Han Jian said. By showing that tentacle feeding was ancestral, the study changes how biologists interpret the early evolution of deuterostomes and the ecological roles these animals played in Cambrian seas.

The fossils are among the few ambulacrarian specimens known from before the appearance of mineralized skeletons, so they provide a rare window into soft anatomy that normally decays. They also demonstrate the continuing scientific value of the Chengjiang Biota and the Maotianshan Shales, which have already produced spectacular soft-bodied fossils from the Cambrian explosion. Each new species from the site adds detail to the picture of how major animal groups first assembled their body plans.

For evolutionary biology more broadly, the study shows that similar feeding strategies can evolve independently in different lineages, and that ancestral conditions cannot always be inferred from living animals alone. The independent evolution of tentacle-based and pharyngeal filter-feeding is a clear example of convergent solutions to the problem of capturing food from water. That lesson extends beyond ambulacrarians to other branches of the animal tree.

Next Up

Researchers will likely search for more Yujingia specimens and compare them with other early ambulacrarians from the Chengjiang Biota and similar deposits. Additional anatomical details, especially of the second appendage set, could clarify how the animal moved and anchored itself. The team's dataset of 505 morphological characters and 100 taxa also provides a foundation for future phylogenetic work as new fossils are described.

The bigger questions concern the timing and tempo of the ambulacrarian split. If Yujingia sits just outside living ambulacrarians, then the last common ancestor probably lived close to 518 million years ago, during the Cambrian explosion. Future finds may push the lineage deeper or reveal intermediate forms that connect the tentaculate body plan to the radial symmetry of starfish and the burrowing habits of acorn worms.