35-7 Sunday, Jan. 5 09:30 - 09:45 Shark Dermal Denticles: Loss and Regeneration Patterns Vary with Body Position and Ecotype COLOMBERO, CR*; WAINWRIGHT, DK; LAUDER, GV; Harvard University; Yale University; Harvard University firstname.lastname@example.org
Dermal denticles – the characteristic scale-type of sharks – are tooth-like structures embedded in the skin. Observation of denticles in a diversity of shark species and body locations reveals “gaps” in the denticle surface pattern where denticles are missing. These missing denticles may be lost as a result of natural replacement cycles or through injury, although little is known about the extent of these gaps in the shark skin surface and how (or if) denticles are replaced. In order to quantify the extent of missing denticles and describe the pattern of denticle replacement, we used four imaging techniques: (1) High-resolution µCT scanning to generate volumetric models, (2) surface profilometry to scan the surface for missing denticles, (3) Scanning Electron Microscopy (SEM), and (4) histology for visualization beneath the skin surface. The percent surface area of missing denticles was calculated for 10 shark species with benthic, coastal mid-water, and pelagic ecologies, and we observed replacement denticles forming and emerging from the dermis and epidermis in the gap regions. Our findings indicate that dermal denticles replace themselves and that this process begins after a scale has been lost. Replacement denticles develop crown-first and are weakly ossified early-on, with a large open pulp cavity and lacking a true root. Thus far, the tails of highly pelagic species including the thresher and mako sharks (Alopias vulpinus and Isurus oxyrinchus, respectively) have the highest percentage of missing denticles of the species surveyed, although even benthic sharks show gaps in the denticle surface and generation of emerging replacement denticles.