Meeting Abstract

P2.129  Saturday, Jan. 5  Shape Changes in the Hyoid Arch of Four Shark Species NOWINOWSKI, I *; BALABAN, J; WILGA, C; University of Rhode Island inowinowski@my.uri.edu

Hyoid depression aids in oropharyngeal expansion and is crucial for suction generation in sharks. The hyoid elements that guide this movement are the paired ceratohyals (CH) and the single, medial, basihyal (BH). These elements are located medial to the lower jaws and when depressed expand the oral cavity. As the coracohyoideus muscle depresses the BH, the CH experiences substantial bending forces. Because of their critical role in the feeding mechanism, the various shapes of the BH and CH are likely adapted for different feeding behaviors. Suction feeders are expected to have a robust hyoid to withstand intraoral forces generated during suction. Whereas bite feeders are expected to have relatively more gracile elements, since rapid hyoid depression is more critical to prey capture. Shape differences in BH and CH elements were studied in bamboo (suction feeders), sandbar (bite feeders), smoothhound (bite), and dogfish (intermediate) sharks using 2D geometric morphometrics. Four landmarks (BH, CH) and 54 or 58 (BH or CH respectively) semilandmarks were digitized on images of the elements. Principal component analysis, partial least squares, and canonical variate analysis were applied to distinguish the shapes of elements and to determine changes among different species. Principal component and partial least squares scores of bamboo elements varied significantly relative to sandbar, smoothhound, and dogfish element scores. The CH in bite feeders was relatively narrower and longer than in suction feeders. The BH of bite feeders had more surface area than suction feeders. Dogfish had characteristics of bite and suction feeders. Consistent with the respective feeding habits, the short and wide hyoid elements of bite feeders were more robust than the narrow and long hyoid elements of suction feeders.