Meeting Abstract

P3.135  Wednesday, Jan. 6  Jaw morphology and structure in lamniform sharks. GOO, B.Y.*; DEAN, M.N.; HUBER, D.R.; SUMMERS, A.P.; University of California, Irvine; University of California, Irvine; University of Tampa; Friday Harbor Labs bgoo@uci.edu

The Lamniformes (Chondrichthyes) are a diverse lineage of highly predatory sharks. Though taxonomically few, they vary widely with regard to trophic morphology and ecology. However, the functional morphology of their feeding apparatus is difficult to study in vivo due to the large size, rarity, and pelagic nature of many of the species. To determine whether and how skeletal performance varies with phylogeny and ecology, we calculated an indirect, shape-based measurement of jaw stiffness (second moment of area (Ina)) from digital cross-sections of CT scans (1mm slice thickness) of adult animals. We examined 6 closely-related lamniform sharks (shortfin mako, sandtiger, salmon, goblin, crocodile, and bigeye thresher) and 2 outgroup species (Orectolobiformes: nurse shark; Carcharhiniformes: blue shark) all of which feed on nektonic prey. By calculating second moment of area along the length of the jaws, we examine the contribution of shape to skeletal flexural stiffness, locating areas of reinforcement and defining their magnitude, and describing the suggested orientation of loading among species. Our results suggest that although these sharks have similar diets, there may be large and mechanically-important differences in the morphologies of their jaws. For instance, we found dramatic increases in Ina toward the rostral tip of the lower jaw in the goblin shark, but toward the caudal end in the shortfin mako. Also, the maximum moment of area reported for goblin shark jaws was 9x greater than that of the mako, indicating a much larger shape-contribution to stiffness in the former species. We discuss results in the contexts of shark phylogeny and the potential mechanical demands of predation.