Manipulations with the wooden model of the Pteronisculus skull

In ray-finned fish, the symplectic together with the palatoquadrate ossification and the hyomandibula forms the suspensorium. However, in paleoniscoids, the suspensorium was not formed, and the symplectic was attached to the lower jaw behind the jaw joint. Modern hypotheses do not take into account certain symplectic morphofunctional features in paleoniscoids. Meanwhile, understanding the biomechanics of the paleoniscoid skull is important for hypothesizing about the evolution of ray-finned fish. Drawing on literature data about the structure of paleoniscoid heads, we conducted a graphical analysis of force distribution in the skull of a basal representative of the genus Pteronisculus during the hyoid retraction and tested it on a wooden skull model. We found previously unrecognized mechanical connection between the expansion of the oropharyngeal cavity and the opening of the mouth. This mechanism may serve as an alternative to the opercular mouth-opening mechanism in modern bony fishes.