Polypterus senegalus SEM Imaging Sample Preparation Protocol Sample Imaging Parameters -Scales were embedded in resin and cured at 60˚ C for 16 hours -Embedded samples were cut using a diamond saw -Samples were polished until cross-section was exposed on a diamond grit wheel -Samples were polished with 16μm, 6 μm, and 1 μm silica nanoparticles on a soft pad and again with 500nm silica nanoparticles on microcloth. -A pair of samples was mounted to the SEM mounting plate with conductive tape. Exposed resin on the samples was coated with conductive paint -Sample was sputter-coated with 5nm of gold in a Denton Vacuum Desk II -Sample was imaged in a JEOL JSM 6060 scanning electron microscope -SEM stage was evacuated to 1-10 μtorr -Images were sampled at 15kV acceleration voltage with a spotsize of 35 Images by Mark Mascaro and Joan Mao

Cracking Within Scale Cross-Section -Cracks vary between 1 and 4 microns across -Roughness of crack edges varies with location

Patterned Pit Regions Sample 1Sample 2 Both samples contained pits in regular intervals parallel to the outer edge of the scale. These pits appear as darkened regions on the micrograph. Pits varied between 20 and 40 microns in size. The pit regions are surrounded almost entirely by cracking. Note that the surface texture of the pits differs from that of the average cross-section. Note also the formation of smaller (micron-scale) pits near the primary pits, connected by lines of fracture. These pitted areas may be pores within the scale.