ROMASCO, Rebecca*; TIMOTHY, Miller; GIBB, Alice C.; Suffolk University, Boston MA; Ashland, Ohio; Northern Arizona University, Flagstaff AZ: The biomechanical basis of intramandibular bending: a novel jaw joint facilitates substrate feeding in the Poeciliidae

To produce the near 180° gape necessary to maximize grazing behaviors, a novel intramandibular joint between the dentary and angular-articular bones of the lower jaw is needed. This joint has evolved independently in a number of teleost groups and illustrates a convergent adaptation that is often associated with increased plant matter in the diet. To explore the functional significance of intramandibular (IM) kinesis, several species of the family Poeciliidae are used. This group possesses a unique, cartilage based, version of the intramandibular joint. Some Poeciliid species have a flange on the dentary which appears to serve as the mechanism to produce IM kinesis; the anterior region of the jaw is pulled caudally and the jaw flexes about the cartilage. We use Poecilia (Molly), Xiphohorus (Swordtail), and Heterandria (Least �killifish�) to represent the lineages that possess this flange. We use Gambusia (Mosquito fish) to represent the taxa without the flange and Fundulus (Killifish) as an out-group species. Using these models we demonstrate that species within the subfamily Poecillinae that possess a posterior directed flange on the medial surface of the dentary will produce intramandibular bending during prey capture to facilitate capturing food items from the substrate.