Figure 3.

Diversity of jaw morphology and the function of jaw levers and linkages in the Labridae. Jaws (a–c) are powerful with a high mechanical advantage (Li/Lo) for jaw closing. Jaws (d–f) are elongate and have a lower force (but higher velocity) transmission. These lever mechanisms are proposed to be homologous and are coded as either continuous or gap-coded states. Jaw (g) is a parrotfish with a novel intramandibular joint, making this jaw mechanism a different character state from the simple levers. (h) Lever model of jaw opening and closing force, in which muscles rotate the jaw and transmit force to the jaw tip. (i) Cranial morphology of Gomphosus varius, demonstrating the jaw's four-bar linkage (j, k) by which the upper jaw is protruded. The lower jaw rotates downward, forcing the maxilla and premaxilla anteriorly to cause jaw protrusion. Scale bars, 5 mm.