Meeting Abstract
Jaw protrusion is a key morphological innovation that enhances suction feeding performance in fishes. Though almost universally present among percomorph fishes, the biomechanical mechanism, direction, and extent of jaw protrusion varies widely. Ponyfishes (Family Leiognathidae) comprise a group of 48 deep-bodied species that inhabit the sandy shores of the Indo-West Pacific Ocean. These fishes are characterized by high jaw protrusion and unusual diversity in the direction of protrusion, with species that protrude their oral jaws in either a ventral, dorsal, or rostral orientation. While ponyfish anatomy has received some attention in the literature, no study has examined the morphological differences underlying jaw protrusion directionality. We measured craniofacial morphology from photographs of 35 cleared and staining specimens representing 21 species, spanning the range of jaw protrusion direction. We then used a functional interpretation of morphology and phylogenetic comparative methods to characterize key differences in craniofacial anatomy and determine the anatomical basis of jaw protrusion directionality within this unique family. We found that the lengths and orientations of many craniofacial elements including the ascending process, mandible, maxilla and jaw joint discriminate between the three oral jaw types. Among the many differences in anatomy, the position of the jaw joint appears to be key to the direction of jaw protrusion as its movement from a more posterior to an anterior position when looking across ventral, rostral and dorsal protruders, significantly changes the orientation of the adducted mandible from a nearly horizontal position in ventral protruders to an upright posture in dorsal protruders.
