SCHAEFER, Justin T*; KOOB, Thomas J; LONG, JR., John H; Univ. of California, Irvine; Shriner’s Hospital for Children, Tampa; Vassar College: Bending mechanics of elasmobranch vertebral columns

The waveform of sinusoidally swimming elasmobranchs depends, in part, on the flexural stiffness of the body, which in turn is presumed to be a function of the material and structural properties of the axial skeleton. We use dynamic three-point bending tests at biologically relevant amplitudes and frequencies to measure the mechanical properties of vertebral columns from three species (Sphyrna tiburo, Carcharinus plumbeus, Rhinoptera bonasus). Two of these species (S. tiburo, C. plumbeus) swim in an axially-undulatory manner while R. bonasus uses pectoral fin oscillations for propulsion. Vertebral morphology varied in length/diameter aspect ratio and amphicoel volume. Stiffnesses were similar between species and through the length of the column, except in R. bonasus. Shear rate had little effect on stiffness of the column. As bending amplitude increased, there was a disproportional increase in force required to bend the column. This was inferred to be the point at which the intervertebral ligaments dominated beam stiffness. This project is supported by NSF grant DBI-0442269.