Evidence for high-performance suction feeding in the Pennsylvanian stem-group holocephalan Iniopera

Suction is an especially effective way of feeding underwater, and adaptations to enhance it have evolved numerous times in jawed vertebrates. The only major living jawed vertebrate group including no specialist suction feeders is chimaeras, a handful of anatomically conservative fish species that feed on hard-shelled prey. Contrastingly, in the Carboniferous (359 to 299 Ma), diverse chimaeras formed a prominent part of aquatic ecosystems. Here, we use three-dimensional-preserved fossils of one of these Carboniferous chimaeras to reconstruct its cranial muscles and argue that it had the forward-facing mouth and expandable pharynx characteristic of high-performance suction feeders. This suggests that in the Carboniferous, some chimaeras were suction feeders in the water column, an ecological niche since monopolized by neopterygian fishes.