According to the scientists behind this amazing discovery, the « dermal teeth » probably help whale sharks, the world’s largest fish, to protect their tiny eyes.
A sharp eye
Whale sharks are known to be gentle giants with moustaches that swim in tropical seas and pick up plankton with their cavernous mouths. Whale sharks can reach a length of up to 15 metres, making them the largest fish in the world. Researchers have recently used radioactive dating techniques to learn that these giant creatures can live for at least 50 years.
According to new research, they also have a sharp eye: their eyes are covered with tiny teeth. The « dermal teeth » are tiny teeth that cover the eyeballs of the whale shark, according to marine biologists at the Okinawa Churashima research centre in Japan, who published their discovery in PLOS One
Teeth like eyelids
Whale sharks and other shark species have dermal teeth that cover their bodies and act like scales, according to the Smithsonian Institution’s Oceanic Portal. The tiny V-shaped fragments reduce drag and turbulence as sharks slide through the water, helping them swim faster. They can also serve as protection against other sharks that might bite them. Eye teeth, however, probably serve as protective armour against the elements.
Whale sharks’ eyes have no eyelids and protrude from each side of the head, making them vulnerable to all forms of aggression. « Considering that these tissues are exposed and that whale sharks do not have eyelids, the surface of the eyes is less protected from mechanical damage than other areas of the body that are covered with mineralised dermal teeth », write the authors of the study. « Thus, covering the surface of the eye with teeth in whale sharks is probably useful to reduce the risk of mechanical damage to the surface of the eye ».
A unique special feature
The team, led by marine biologist Taketeru Tomita of the Churashima Foundation Research Centre in Okinawa, Japan, studied the eyes of live and dead sharks that had washed ashore. They discovered that a single eyeball of a whale shark could have more than 3,000 teeth, which are clustered around the iris. Looking under a microscope, the researchers described the teeth as having an « oak leaf » shape. Some of them even look like human molars.
Scientists have also noted that whale sharks have the ability to partially retract their eyeballs in their skull. These two protective mechanisms (retractability and small teeth) suggest that their eyes may be more important to their survival than previously thought. Indeed, it was hypothesized that cetaceans rely more on smell than sight to navigate their environment because whale sharks have relatively small eyes. However, the highly protected functions of the whale shark’s eye seem to suggest the importance of vision in this species.