Meeting Abstract

76.5  Sunday, Jan. 6  Morphology of a picky eater: A novel mechanism underlying premaxillary protrusion and retraction within Poeciliidae HERNANDEZ, L.P.*; FERRY-GRAHAM, L.; GIBB, A.C.; George Washington University; Moss Landing Marine Labs; Northern Arizona University phernand@gwu.edu

Upper jaw protrusion is hypothesized to improve feeding performance in teleost fishes by enhancing suction production and the stealth of a feeding event. However, many cyprinodontiform fishes (mid-water feeders, such as mosquitofish, killifish, swordtails, mollies, and pupfish) use upper jaw protrusion for �picking� prey out of the water column or off the substrate; this feeding mode may require improved jaw dexterity, but does not require increased suction production. We describe functional changes to the bones, muscles and ligaments of the anterior jaws in a phylogenetic cross-section of cyprinodontiform species. Most species possess a novel ligament that connects the premaxilla of the upper jaw to the lower jaw, coupling depression of the lower jaw with protrusion of the upper jaw and effecting a previously unknown mechanism of jaw protrusion. This mechanism is further refined in some poeciliids, where direct muscular control of the premaxillae apparently facilitates scraping or nipping material from the bottom. We posit that, within Cyprinidontiformes, this ligament may increase premaxillary protrusion distance, and enhance the use of the anterior jaws as forceps for picking individual prey items since the upper and lower jaws move in a coordinated fashion. These two features�a unique ligament and a novel insertion of a major jaw adductor�appear to enable a functional transformation of the anterior jaws in derived poeciliids. We postulate that this unusual mechanism of premaxillary protrusion and retraction allows cyprinodontiform fishes to selectively pluck specific food items from the water column, surface or bottom.