Deep ghost sharks push teeth on their forehead, and scientists finally know why

Male ghost sharks use tooth stems on their forehead for mating. Fossil and genetic evidence proves that they are real teeth, with evolutionary flexibility.

Men’s “ghost sharks”, strange deep fish known as Chimaeras and closely linked to sharks and rays, have a strange cane that projects with their forehead and is covered with clear and retractable teeth. New research shows that these are not simple imitations but real rows of teeth that develop outside the mouth.

The unusual structure, called tenaculum, is only found in men and plays a role in reproduction. It represents the species“Only distinct teeth and seems to help males to keep women during mating, just as sharks use their mouths and teeth for the same purpose.

“If these strange chimaeras bang teeth in front of their heads, it makes you think more generally about the dynamism of the development of the teeth,” said Gareth Fraser, Ph.D., professor of biology at the University of Florida and the main study of the study. “If the Chimaeras can make a set of teeth outside the mouth, where we could find teeth?”

Fossil and modern proof of dental stems

Researchers from Washington University and the Chicago University examined both fossilized remains and living ghost sharks to unravel the mystery. A fossil, dating from 315 million years, revealed a ténaculum linked to the upper jaw which transported teeth surprisingly similar to those found inside the mouth. Modern specimens from Puget Sound displayed the same development of head -based teeth observed in the jaws of current sharks. Genetic analysis also confirmed that these structures activated the same genes responsible for the production of oral teeth.

“What we have seen is that the teeth of this strange appendage are very similar to rows of shark teeth. The possibility of transferring the teeth to this appendage, probably in the mouth,” said Fraser. “Over time, the tenaculum has shortened but has retained the ability to make oral teeth on this front appendage.”

Fraser has collaborated with Karly Cohen, Ph.D. of Washington, and Michael Coates, Ph.D., of Chicago on the study, which was published this week in the Proceedings of the National Academy of Sciences.

Distinguish teeth from skin denticles

Specialists in the evolution of sharks and anatomy were fascinated by the stems covered with teeth emerging from the front of ghost sharks. Their main question was whether the tenaculum contained real teeth linked to those of the mouth, or if it looked more closely to the tooth scales that cover the skin of sharks and ghost sharks.

The computed tomography of the fossils and modern chimaeras have given scientists scientists and detailed detailed information on the development of the teeth of the tenaculum, which looked remarkably to the teeth of today’s sharks. The highlight in the coffin came from genetic evidence. The teeth of the Tenaculum express genes found only in real teeth, never in the denticles of the shark skin.

Evolutionary DIY and surprising adaptation

“What I think is very neat in this project is that it provides a fine example of evolutionary DIY or” DIY “, said coats, a biology professor at the University of Chicago. “We have a combination of experimental data with paleontological evidence to show how these fish have co -opted a pre -existing program for the manufacture of teeth to make a new device essential for reproduction.”

Cohen, a postdoctoral researcher in the Friday Harbor Labs of the University of Washington and the first author of the newspaper, said that scientists had never spotted teeth outside the mouth in this way before.

“Tenaculum is a relic of development, not a unique bizarre, and the first clear example of a toothed structure outside the jaw,” she said.

The bizarre path of a mouth full of teeth with the forehead used for mating shows the impressive flexibility of evolution, according to the researchers, always ready to reuse structures for new strange and unexpected uses.

“There are still a lot of surprises in the depths of the ocean that we have not yet revealed,” said Fraser.

Reference: “Teeth outside the jaw: Evolution and development of the clasper with toothed heads in the chimaeras” by Karly E. Cohen, Michael I. Coates and Gareth J. Fraser, September 4, 2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / PNAS. 2508054122

Never miss a breakthrough: join the Scitechdaily newsletter.