So sharks, like humans, are largely defined by a single piece of anatomy – their teeth.
For years, it was widely accepted that white sharks are born with pointy teeth, perfect for grabbing into slippery fish (their primary diet at such a young age). It was believed that when the animal reaches somewhere in the region of three metres in length, that those teeth are progressively replaced with much broader ones, more suited to the dissection of marine mammals (dolphins and seals).
This transition from one tooth shape to another is called an ‘ontogenetic shift’, encompassing a change in both diet and tooth shape.
Georgia French (founder of UK Charity Shark Stuff and lead on this particular research project) felt this might not be entirely accurate, having recognised published data and scientist accounts of very large sharks with pointed teeth.
This marked the birth of the project, as Georgia wanted to focus specifically on shark teeth and whether it is a universal rule, that the accepted ontogenetic shift would always take place.
Georgia started working with Marine Dynamics Shark Tours and the Dyer Island Conservation Trust, jumping on the white shark cage diving boat and taking photographs of their teeth when breaching the surface of the water, mouth agape.
To determine whether a tooth was broad or pointy in objective terms, she would divide its width by its height. If the number was high, the tooth was pointy, if the number was low, the tooth was broad.
The total length of each shark was taken into consideration so it would be cross-referenced with tooth sizes.
Differences between the sexes – who would’ve thought?
Georgia discovered that while the generally accepted ontogenetic shift was indeed evident in male white sharks, pointed teeth remaind present on female sharks of all sizes. Likewise, while the angle of upper teeth on male sharks changed over time, females did not.
What this indicates, is that males and females target different prey as they age, or that tooth shape isn’t related to diet at all. Potentially, it might also mean that the changing angle of top-row teeth in male sharks is an adaptation for mating.
That’s the jist of it, you can read in far more (interesting) details on Georgia’s SharkStuff Blog.
My responsibilities on this project were largely the same as on Gauging The Threat, identifying and cataloging individual sharks using Darwin.
I likewise provided some additional technical support/assistance to Georgia, eventually going to to contribute my branding and web design services to SharkStuff.