Scientists solve mystery of 500-million-year-old ancient fossil

A recent study conducted by our Earth Sciences department has unveiled a surprising revelation about a mysterious fossil dating back to the Cambrian period, over 500 million years ago.

Initially believed to be an early mollusc—a group that includes creatures like snails and clams—the fossil, Shishania aculeata, has now been identified as a sponge-like organism known as a chancelloriid.

Published in the journal Science, this discovery offers new insights into the evolution of some of the earliest forms of animal life.

Not a snail, but a sponge relative

The Shishania fossil was initially found in southern China and appeared to have a foot-like structure and protective spines—traits that led scientists to classify it as a mollusc relative.

However, recent research reveals that many of these characteristics were artifacts of fossil preservation rather than true anatomical features.

Upon examining better-preserved specimens, researchers discovered that the so-called "foot" was actually the animal’s internal structure exposed by splitting. In reality, its body resembled a spiny sac rather than that of a mollusc.

Clues to an ancient group

The newly examined fossils studied by the research team reveal that Shishania has several traits in common with chancelloriids—unusual, sac-like creatures that lived attached to the ocean floor and lacked a head, mouth, or internal organs.

These animals were covered in hollow spines, which may have served a defensive purpose.

This finding helps bridge a gap in the fossil record and provides insight into how chancelloriids may have gradually developed more complex body structures.

A clearer picture of early life

Studying Shishania gives scientists deeper insight into the ‘Cambrian explosion,’ a pivotal period when many animal groups first emerged.

It also highlights how fossil interpretations can be misleading and how ongoing discoveries continue to refine our understanding of early life on Earth.

Fossils like Shishania serve as a reminder that evolution often holds unexpected twists and that science is always evolving to better explain the natural world.