The fish that has teeth on the forehead

I know adult male mottled rat fish. A team led by the University of Washington has identified teeth at the top of its head. Use them to hold the female in mating. The fish that has teeth on the forehead is a rarity of the natural world.

The mottled rat fish is a species similar to a native shark of the Northeast of the Pacific Ocean. It has teeth rows on the top of the head. They cover a cartilaginous appendix called Tenacle.

Non -oral teeth

«It is an incredible and absolutely spectacular characteristic. It reverts the old assumption in evolutionary biology that teeth are strictly oral structures ». Karly Cohen, a researcher at the University of Washington, says it in a statement. «Tenacle is a development relic. And the first clear example of a dentated structure outside the jaw ».

The mottled rat fish belongs to a category of cartilaginous fish called chimeras. They separated from sharks in the evolutionary tree millions of years ago. With an approximate length of 60 cm, the mottled rat fish receives its name for its long and thin queues. They represent half of their length. Only adult males have a tenacle decorating their forehead. At rest, it looks like a small white peanut between the eyes. In erection, the tenacle has a hook and spikes with teeth.

The males extend their tenacle to intimidate their competitors. During mating, they hold females by the pectoral fin to avoid separating. Both males and females begin to develop a tenacle from an early age. In females, it never materializes or mineralizes. But evidence of an early structure persists.

Dispersed genetics

The new teeth settle in a band of fabric called dental sheet, present in the jaw, but never documented elsewhere. "When we saw the dental sheet for the first time, we were speechless," Cohen said. "It was very exciting to see this crucial structure outside the jaw."

In humans, the dental sheet disintegrates after permanent teeth grow. But many vertebrates retain the ability to replace them. Sharks, for example, have a "constant conveyor chain" of new teeth. The fish that has teeth on the forehead shows it. The identification of this structure was a overwhelming proof that the teeth of the have they are really teeth and not leftover denticles. Genetic evidence also supported this conclusion.