Meeting Abstract

P1.39  Jan. 4  Morphometric Head Shape Comparison Among Hammerhead Sharks (Sphyrnidae). MARA, K.R.**; MOTTA, P.J.; Univ. of South Florida, Tampa; Univ. of South Florida, Tampa kmara@mail.usf.edu

The laterally expanded and dorsoventrally compressed pre-branchial cephalofoil of hammerhead sharks (Sphyrnidae) displays disparate shapes and sizes. Within sphyrnid sharks, expansion of the cephalofoil ranges from the extremely wide high aspect ratio head of Eusphyra blochii (40-50% of TL) to the moderately expanded head of Sphyrna tiburo (18-25% of TL). A landmark based geometric morphometric analysis was performed on E. blochii, S. mokarran, S. lewini, and S. tiburo, representing a continuum of head shape and size. Landmarks were chosen that represent mouth, eye, and naris position, as well as overall shape of the cephalofoil. The transition from E. blochii to the S. mokarran and S. lewini functional complex is characterized by a relative decrease in cephalofoil lateral expansion, a rostral shift and enlargement of the mouth, lateral shifting of the nares, and movement of the eye rostrally and medially. The transition from the S. mokarran and S. lewini functional complex to the most derived S. tiburo involves a decrease in lateral expansion of the head, shifting of the mouth position caudally and a decrease in mouth size, medial relocation of the nares, and medial shifting of the eyes. During this transition there is also slight anterior rostral expansion. Changes in head morphology are discussed in relation to the concomitant changes in the feeding and sensory apparatuses.