GRUBICH, Justin R; WESTNEAT, Mark W; The Field Museum of Natural History; The Field Museum of Natural History: Biomechanical Modeling of Pharyngeal Jaw Bite Force in Sciaenid Fishes

Pharyngeal jaws in many fishes process prey items for digestion by biting or crushing them with high compressive forces. Engineering principles of four-bar linkages were used to create a mechanical model of pharyngeal jaw biting in sciaenid fishes. Computer models of lever and linkage mechanics of anterior jaws were modified to define musculoskeletal couplings of the upper branchial arches in the red drum, Sciaenops ocellatus. Bite mechanics in the upper jaw are modeled as two medially connected bilateral four-bar linkages that have an oblique planar orientation to the long axis of the body. A single pharyngeal linkage includes the neurocranium, the levator posterior (LP), 3rd pharyngobranchial (PB3), and 4th epibranchial (EP4). The output of this linkage results in ventral depression of PB3. Two input links are examined in the model the LP and associated muscles, and EP4. By altering input link characteristics, the model allows us to simulate variation in kinematic transmission (KT) of upper jaw depression. A key component of this model is the input link, EP4 that is proposed to act as a 1st class lever. As such, bone dimensions and attachment angles of levator muscles influence toothplate displacement and force transmission of the bite. Variation in this input link therefore has predictable consequences for upper jaw bite performance. A survey of mechanical advantage (MA) in 4th epibranchial bones for drum species (Sciaenidae) revealed an ecomorphological pattern where species with predominantly soft prey diets have MA�s < 1 while durophagous species have MA�s > 1.