About half a billion years ago, a bizarrely shaped creature with a length of up to 4 cm lived in the oceans of the world. The species, called Stylophoran, had an unusual appearance consisting of a single long appendage and a flat body, making it difficult for scientists to determine where they fall on the animal lineage. After more than 150 years of mystery, a new study has the answer.
At the heart of the mystery was the unusually long paddle appendage of Stylophoran. Scientists have speculated whether the appendage was something like a tail or whether it was used for feeding; The skeletal anatomy of the creature was not enough to fix the debate, but its surviving innards are.
It turns out that stylophorans were echinoderms, the ancient relatives of today's starfish, sea urchins and sea cucumbers. The determination was based on high quality fossils found in Morocco, which were preserved in the iron mineral pyrite. The long appendage was not a tail but resembled the arm of a starfish.
This discovery was made possible by mapping the fossil iron and using it to analyze the structure of the appendix, especially the soft tissues, which often do not petrify. The arm-like appendage featured a water-vessel system not unlike a modern starfish.
The appendage would have been used to help the shallow creature move and eat. One notable difference between the stylophorans and the starfish is, of course, the lack of a five-rayed symmetry from which they may have evolved. The full study can be read here.