Initially interpreted as a primitive Cambrian mollusk, Shishania aculeata — a 500-million-year-old spine-covered fossil present in China’s Yunnan province — is in truth a distant relative of sponge-like creatures often known as chancelloriids, based on a group of paleontologists from Yunnan College, Yuxi Regular College and Durham College.
Shishania aculeata. Picture credit score: Yang et al., doi: 10.1126/science.adv463.
Shishania aculeata was beforehand believed to show mollusk-like options together with a muscular foot and specialised mineralized spines.
Nevertheless, the brand new fossils present that the traditional animal carefully resembles chancelloriids — bag-like animals coated in defensive spines, anchored to the Cambrian sea flooring.
“We found that lots of the options beforehand thought to point molluskan affinity had been in truth deceptive artifacts of fossilization,” mentioned Durham College paleontologist Martin Smith and colleagues.
“For instance, buildings taken to be a ‘foot’ had been revealed to be the results of distortion through the fossil’s preservation, a course of described as a taphonomic phantasm.”
“These historic fossils turned out to be masters of disguise. Shishania aculeata appeared to indicate all of the hallmarks we’d anticipate of an early mollusk ancestor.”
“However because it dawned on us that the mollusk-like outlines of the fossil materials represented a piece of fossil origami, we had been led to re-examine one another a part of the interpretation in flip.”
“The thriller began to unfurl as soon as we discovered chancelloriids preserved in a really comparable approach in the identical rock unit.”
The reclassification of Shishania aculeata is especially vital as a result of chancelloriids are an enigmatic group recognized solely from Cambrian rocks, disappearing round 490 million years in the past.
Although superficially resembling sponges, their our bodies are adorned with star-shaped spicules whose intricate microstructure hints at attainable connections to extra advanced animals.
With its very simple spines, Shishania aculeata means that chancelloriids developed their ornate spicules from scratch, reasonably than adapting them from pre-existing skeletal buildings.
That tells one thing profound about how advanced physique plans developed through the Cambrian explosion — the evolutionary burst that gave rise to all fashionable animal teams.
“When Shishania aculeata was first described final 12 months, I used to be thrilled — it appeared to match the early ‘slug-like’ animals I’d all the time imagined,” Dr. Smith mentioned.
“However the brand new materials pressured me to re-evaluate the whole lot.”
The additional evaluation revealed patterns as soon as thought to mirror molluskan biology corresponding to a ‘paintbrush-like’ association within the spines had been really preservation artifacts, as the identical patterning occurred randomly throughout the fossil.
Compression and deformation throughout fossilization had additionally made the straightforward cylindrical animals seem extra anatomically advanced than they honestly had been.
This reinterpretation has implications not just for understanding chancelloriids, but additionally for figuring out different ambiguous Cambrian fossils.
It reopens questions on early mollusk evolution and cautions in opposition to over-interpreting ambiguous fossil options.
“On the similar time, it helps solidify our image of chancelloriid origins and provides us contemporary perception into how evolutionary novelty emerged,” the researchers mentioned.
Their paper was printed right this moment within the journal Science.
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Jie Yang et al. 2025. Shishania is a chancelloriid and never a Cambrian mollusk. Science 388 (6747): 662-664; doi: 10.1126/science.adv463
