A mysterious fossil that puzzled scientists for years has finally been identified—and the findings are shaking up what we know about early animal evolution.
The fossil, known as Shishania aculeata, was discovered in 500-million-year-old Cambrian deposits in Yunnan Province, southern China.
This region is famous for its exceptionally well-preserved fossils that provide rare glimpses into the distant past.
When Shishania was first studied, it was thought to be one of the earliest mollusks, potentially an ancestor of modern snails, slugs, and clams.
Its fossilized remains seemed to show features like a muscular foot and mineralized spines, which are characteristic of mollusks. However, a new study led by researchers from Durham University and Yunnan University has completely changed this view.
The team, using better-preserved fossils and advanced imaging techniques, discovered that Shishania is not a mollusk at all. Instead, it belongs to a group of sponge-like creatures called chancelloriids.
Chancelloriids are an ancient group of animals that lived during the Cambrian period and disappeared around 490 million years ago.
Unlike sponges, which are soft and porous, chancelloriids were covered in spiny armor that protected them as they sat anchored to the seafloor.
Their bodies were adorned with star-shaped spicules—unique skeletal structures that make them easily recognizable. For years, chancelloriids have been a bit of a mystery to paleontologists, as their relationship to other animals has never been fully understood.
The breakthrough came when the researchers examined new fossil specimens from the same rock layers where Shishania was found. Advanced imaging revealed that the supposed mollusk-like features were actually misleading.
What had been interpreted as a “foot” turned out to be a result of distortion during fossilization—a phenomenon researchers described as a “taphonomic illusion.” This means that the fossil’s structure had been warped over millions of years, giving it the appearance of something it was not.
Dr. Martin Smith, a co-author of the study from Durham University, described the fossils as “masters of disguise.” He admitted that when Shishania was first discovered, he believed it confirmed his own theories about early mollusk ancestors.
The fossil seemed to match the early “slug-like” animals he had imagined. However, the new evidence forced him and his team to re-examine everything they thought they knew. Dr. Smith explained that the mollusk-like features were just the result of fossilization, not biological traits.
One of the most telling clues came when the team found chancelloriid fossils preserved in nearly the same way in the same rock layers. This discovery suggested that Shishania was not unique but part of the chancelloriid family, changing its place in the evolutionary tree.
The reclassification of Shishania as a distant relative of sponges has important implications for understanding early animal evolution. It challenges previous ideas about what early mollusks looked like and emphasizes the need for caution when interpreting fossil features.
The findings also deepen our understanding of chancelloriids, hinting that their complex spiny structures developed independently rather than evolving from pre-existing skeletons.
Dr. Smith noted that this reinterpretation not only helps clarify the origins of chancelloriids but also opens up new questions about other ambiguous Cambrian fossils. It highlights the importance of China’s fossil-rich regions and the value of international collaboration in solving ancient mysteries.
The study not only reshapes our understanding of these ancient creatures but also serves as a reminder of how much we still have to learn about life’s earliest chapters. As new fossils emerge and technology advances, scientists are getting closer to piecing together the puzzle of Earth’s distant past.
Source: Durham University.
