Meeting Abstract

P2.128  Saturday, Jan. 5  Mechanical design in fin whale mandibles SHADWICK, R.E.*; WHALE, J.C.; LIN, S.C.; GOLDBOGEN, J.A.; PYENSNON, N.D.; Univ of British Columbia; Univ of British Columbia; Univ of British Columbia; Cascadia Res. Collective; Smithsonian Inst. shadwick@zoology.ubc.ca

Mandibles in large rorquals such as fin and blue whales are highly modified to function as load bearing elements that support the engulfment apparatus and the large forces experienced during lunge-feeding. Each mandible typically represents ~20% of the total body length and, as such, these bones represent the largest single ossified elements in the animal kingdom. Here we explore two questions regarding their mechanical design. 1. Considering the high aspect ratio and high degree of curvature, are the mechanical properties of the mandible uniform or heterogeneous along its length? 2. How is the compressive stiffness related to mineral density distribution within the structure? From the mandible of a freshly dead 18m fin whale we cut sections from eight locations along the entire length, and made density maps of each by CT scanning. Test samples 1 cm in diameter were removed with a plug cutter mounted in a drill press. We determined wet density, dry density, compressive stiffness, breaking strength, and mineral content of each. The results show two very distinct regions; the dense cortical bone (max. of 1.99g/cc) is located in a relatively narrow peripheral layer while much less dense and oil filled trabecular bone (min. of 0.91g/cc) occupies the central core. Compressive stiffness is strongly correlated with mineral content and density, with modulus of the cortical layer ranging from 1-8GPa compared to only 0.05-0.40GPa in the trabecular bone. It appears likely that the superficial cortical layer is the main load bearing element, while the mechanical contribution from the central trabecular region is minimal, somewhat reminiscent of avian long bones.