An article published in the journal “Nature” describes a research on Haplophrentis carinatus and in general of the group of hyoliths, animals that lived during the Cambrian period, starting from about 530 million years ago. A team of researchers from the University of Toronto found evidence that these animals are related to the brachiopods (phylum Brachiopoda), marine invertebrates that existed at the time of which some species still exist today.
Haplophrentis carinatus was one of the many animals that lived in the Cambrian that were very different from the present ones but it’s not the strangest of them. It was in many ways similar to a mollusc for its long conical shell but on its front it had two side curved structures that maybe used as stabilizers as it moved and as anchores to the seabed. These structures were present only in some hyolith species.
Hyoliths were very small, not longer than a few centimeters but a lot of specimens were found in the Burgess Shale, one of the most extraordinary fossil deposits in the world. Nevertheless, their classification and the relations with other groups of animals caused considerable debates among paleontologists. Maybe they were benthic animals, meaning inhabitants of sea beds but a big problem until now was that the fossil record showed their external appearance but not their internal anatomy.
The discovery of new specimens of hyoliths in the Burgess Shale could solve the issue because some of their soft tissue fossilized as well. It’s an exceptional event that occurred thanks to the conditions in that area, which were favorable to such a complete fossilization.
Joseph Moysiuk, who led this research, received the Best Poster Award at the Paleontological Association meeting held in France last month even if he’s still a student. It’s a great achievement due to the fact that he offered a solution to a mystery that lasted for many decades considering that Haplophrentis carinatus was described for the first time at the end of the 19th century.
Studying the new hyolith specimens, Joseph Moysiuk and his team were able to examine their anatomical feeding structure. That’s how they discovered that it’s a row of flexible tentacles that extend from its mouth, which is contained in the cavity between the upper and lower valves. Only brachiopods have a feeding structure closed between valves of that type.
This discovery is strong evidence that brachiopods and not molluscs are hyoliths’ closest relatives. It also suggests that hyoliths fed on organic materials suspended in water like today’s brachiopods, which sweep them into their mouths using their tentacles.
Maybe this research put an end to a lot of discussions on the classification of hyoliths. Many creatures that lived in the Cambrian are still difficult to classify but the discovery of new fossils and the adoption of new technologies to examine them can be of great help to paleontologists.
