Odd creatures called hyoliths, which existed during the Cambrian period, have finally been scientifically classified. A team of researchers studied their fossils and found that they most closely resembled lophophorates—a group of invertebrates that share a specific type of feeding organ. The details were just published in the journal Nature.
Hyoliths, strange invertebrates that were first discovered 175 years ago, have long puzzled scientists. They were never properly classified and were thought to be related to molluscs, a phylum that includes snails, octopuses, squid, and clams. Hyoliths were tiny creatures, no longer than four centimeters, and they were protected by cone-shaped shells made of calcium carbonate. Hyolith fossils have been dated back to 530 million years ago and they existed for 280 million years before going extinct during the Paleozoic era. Scientists have had a difficult time sorting hyoliths taxonomically, partially because their soft tissues don’t preserve well during fossilization.
Thanks to newly discovered fossils, a team of researchers was able to solve the mystery of the hyolith. The team studied fossils that contained preserved soft tissue and noticed something interesting about their feeding organs. Their mouths contained tentacles and resembled the mouths of lophophorates. As the team continued to study the anatomy of the new fossils, it became even clearer that they were most closely related to brachiopods, phoronids, and tommotiids—a group that mostly includes extinct animals. The presence of a lophophore, a feeding organ surrounded by tentacles that filters food items out of water, is the defining feature of the group. Hyoliths have now been added to Lophophorata.
The team’s findings provide new insights into the evolution of lophophorates, a group that mostly contains extinct filter feeding invertebrates. The discovery of well-preserved fossils allowed a team of paleontologists to properly classify hyoliths, solving a long-standing taxonomical mystery.
Moysiuk et al. Hyoliths are Palaeozoic lophophorates. Nature (2017).