Meeting Abstract

43.3  Sunday, Jan. 5 10:45  Shape Changes in Hyoid Arch Elements in Four Shark Species NOWINOWSKI, I*; BALABAN, J; WILGA, C; University of Rhode Island; University of Rhode Island ; University of Rhode Island inowinowski@my.uri.edu

Hyoid depression aids in oropharyngeal expansion and is crucial for suction generation in sharks. The hyoid arch is medial to the jaws and is made up of paired hyomandibular cartilages (HY) dorsally, paired ceratohyal cartilages (CH) ventral to the HY, and a single, medial basihyal cartilage (BH) that interconnects the two sides. The coracohyoideus muscle pulls the BH down and back, which in turn swings the CH down and back, creating substantial bending forces in the CH. Suction feeders are expected to have robust hyoid elements to withstand suction forces. Bite feeders are expected to have relatively more gracile elements, since strong, rapid jaw adduction is more critical to prey capture. Shape differences in BH, CH, and HY elements were studied in bamboo (suction feeders and crush processors), sandbar (bite feeders and bite processors), smoothhound (bite capturers and crush processors), and dogfish (intermediate feeders and bite processors) sharks using 2D geometric morphometrics. Two to four landmarks were digitized on the lower and upper cranial articulation and 46 to 58 equidistant semi-landmarks were digitized along the outline. Covariance matrices, procrustes coordinates, principal component analyses, and discriminant analyses distinguish the shapes of elements and determine changes among species. The CH and BH are similar in the two species with similar capture style (robust in suction, slender in bite), while the HY is similar among the species with similar processing style (extra processes on bite compared to crush).