ABSTRACT
Parrotfishes feed by scraping hard rocky surfaces to obtain material that they grind into a fine slurry with their pharyngeal jaws. Their unique role as disruptors of benthic communities and bioeroders of the reef is closely linked to three major innovations of the feeding apparatus that are described here. The parrotfish pharyngeal jaws include elaboration of the fourth epibranchial bones to stabilize extensive anterior-posterior movements of the upper jaws during the milling actions. The oral jaws of most parrotfish species are armed with a cutting, beak-like edge that allows the distinctive scraping action during feeding. Within one group of parrotfish there is a novel intra-mandibular joint that substantially alters the mechanics of jaw movements. Patterns of morphological diversity of the feeding apparatus of parrotfishes reveal a major axis of diversity that contrasts species with large muscles, high jaw protrusion and a wide mouth, with species with small structures. Studies show that the rates of evolution of oral jaw traits are elevated in the clade that exhibits the intra-mandibular joint, indicating a role for this innovation in spurring additional functional diversity.
