Ancient chimaeras were suction feeders, not shell crushers, new research shows

A rare three-dimensional fossil of an ancient chimaera has revealed new clues about the diversity of these creatures in the Carboniferous period, some 300 million years ago.

Research led by the CR2P and MECADEV (Muséum national d'histoire naturelle, MNHN) and the University of Birmingham has shown that an ancient relative of chimaeras—jawed vertebrates that are related to sharks and rays—fed by sucking in prey animals underwater.

The fossil, from a genus called Iniopera, is the only suction feeder to be identified among chimaeras, and quite different from living chimaeras, which feed by crushing mollusks and other hard-shelled prey between their teeth. The research is published in the journal PNAS.

Dr. Richard Dearden, lead researcher on the paper at the University of Birmingham, said, "Being able to identify Iniopera as a suction feeder sheds light on the diverse role of chimaeras in these early ecosystems. In particular, it suggests that in their early evolutionary history, some chimaeras were inhabiting ecological niches that are now monopolized by ray finned fishes—a far cry from their modern life as specialized shell-crushers."

Because chimaeras' skeletons are composed mostly from cartilage, their fossil remains are often flat and therefore difficult to extract information from. From studying the diverse body and tooth shapes, however, researchers already knew that there were far more, more varied species of chimaera living in the Carboniferous than there are today.

Using 3D imaging techniques, the team reconstructed the head, shoulder and throat skeleton of the fossil. They then estimated the location of major muscles and found the anatomy was poorly suited to crushing hard shelled prey. Instead, the researchers believe the animal was more likely to have used the muscle arrangement to expand the throat to take in water and a forward-pointing mouth to orient towards prey.

Suction feeding is a technique used by many animals that live underwater. It involves generating low pressures in the throat to pull in water and prey. To do this effectively, the animal needs to be able to rapidly expand its throat, and point its mouth forward towards prey items. Numerous different aquatic jawed vertebrates, such as ray-finned fishes and some turtles have evolved specialized anatomies to help them suction feed more effectively.

The suction feeding theory proposed by the team also fits with other evidence including arthropods preserved inside the stomach of other specimens.

• Référence : Dearden RP, Herrel A, Pradel A. 2022. Evidence for high-performance suction feeding in the Pennsylvanian stem-group holocephalan Iniopera. The proceedings of the National Academy of Sciences. DOI : https://doi.org/10.1073/pnas.2207854119