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Protrusible Jaws
Protrusible jaws are a novelty in Teleosti, a subgroup of Actinopterygians, that has independently evolved at least five times. Species with protrusible jaws are able to extend their premaxilla anteriorly decreasing the space between the predator and prey. There are four different mechanisms of how fish are able to protrude their premaillary bone via differences in ligamentous linkages within the skull. These four models are 1) Mandibular depression model 2) Twisting maxilla model, 3) Decoupled model, 4) Suspensorial abduction model. In the mandibular depression model the depression of the lower jaw (mandible) pulls or pushes the premaxilla into protrusion via force transmission through ligaments and tendons connected to the upper jaws (e.g. Cyprinus, Labrus). The twisting maxilla model involves the depression of the mandible causing the maxilla to twist about the longitudinal axis which causes the protrusion of the premaxilla (e.g. Mugil). For the decoupled model, protrusion of the premaxilla is accomplished through elevation of the neurocranium causing the premaxilla to move anteriorly. In this model the movements of the neurocranium are not coupled with the kinematics of the upper jaw (e.g. Spathodus erythrodon) allowing for more versatility and modularity of the jaws during prey capture and manipulation. The final model, the suspensorial abduction model, involves the lateral expansion of the suspensorium (a combination of the palatine, pterygoid series, and quadrate bones) pulling on the palatopalatine ligament which causes the premaxilla to protrude anteriorly (e.g. Petrotilapia tridentiger). The mandibular depression model is able to explain the majority of fish cranial mechanics observed within actinopterygians. However, these models are not mutually exclusive with some cranial mechanics being explained by multiple models (e.g. Petrotilapia).

Actinopterygians
Actinopterygians exhibit a large diversity in the complex system of their feeding apparatus (Figure 3). These fishes have various dietary strategies from herbivores, planktivores, and carnivores, with some specific diets involving scale-eating. To capture prey, species employ differing feeding strategies like biting and ram feeding, but no other feeding behavior is as pervasive as suction feeding (Lauder, 1985, 1982). Suction feeding is a highly coordinated behavior achieved by the dorsal rotation of the neurocranium, lateral expansion of the suspensorium, and the depression of the lower jaw and hyoid (Figure 4). Suction feeding leads to successful prey capture through rapid movements creating a drop in pressure in the buccal cavity causing the water in front of the mouth to rush into the oral cavity (Lauder, 1980a), entrapping the prey in this flow. This mode of feeding has two main phases: expansion and compression (Lauder, 1982). The expansion phase involves the initial opening of the jaws to capture prey. These movements during the expansion phase are similar across all suction feeders with variations in the kinesis of the skull. During the compression phase the jaws close and water is compressed out of the gills.