Around half a billion years ago, the world's oceans were home to a bizarrely shaped creator measuring up to 4cm in length. Called stylophoran, the species had an unusual appearance that included a single long appendage and a flat body, making it difficult for scientists to determine where the falls on the animal family tree. After more than 150 years of mystery, the new study has the answer.
The stylophoran was unusually long paddle-like appendage at the heart of the mystery. Scientists have speculated whether the appendage was something like a tail or if it was used for feeding; the creature's skeletal anatomy was enough to settle the debate, but its preserved innards are.
It turns out that stylophorans were echinoderms, the ancient relative of modern-day starfish, sea urchins, and sea cucumbers. The determination was made using high-quality fossils discovered in Morocco, one preserved in the ferrous mineral pyrite. The long appendage was a tail, but something similar to the arm of a starfish.
This discovery was made possible by mapping the fossils' iron and using it to analyze the appendages, particularly the soft tissues that often do not fossilize. The arm-like appendage featured a water vascular system not unique to modern starfish.
The appendage would have been used to help the flat creature move around and eat. A notable difference between the stylophorans and starfish, of course, is the lack of five-rayed symmetry, which they may have evolved away from. The full study can be read here.