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Deep-Sea Ghost Sharks Grow Teeth on Their Foreheads, and Scientists Finally Know Why
Scitech Daily ^ | September 21, 2025 | Eric Hamilton, University of Florida

Posted on 09/22/2025 5:50:58 AM PDT by Red Badger

Caught male Spotted Ratfish (Hydrolagus colliei) showing the [extended/erect] frontal clasper (tenaculum) on the front of the head. Credit: Gareth J. Fraser, University of Florida

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Male ghost sharks use tooth-studded rods on their foreheads for mating. Fossil and genetic evidence prove they are true teeth, showcasing evolutionary flexibility.

Male “ghost sharks,” eerie deep-sea fish known as chimaeras and closely related to sharks and rays, have a strange rod that projects from their foreheads and is covered with sharp, retractable teeth. New research shows these are not simple imitations but actual rows of teeth that develop outside the mouth.

The unusual structure, called a tenaculum, is found only in males and is thought to play a role in reproduction. It represents the species’ only set of distinct teeth and appears to help males hold onto females during mating, much like sharks use their mouths and teeth for the same purpose.

“If these strange chimaeras are sticking teeth on the front of their head, it makes you think about the dynamism of tooth development more generally,” said Gareth Fraser, Ph.D., a professor of biology at the University of Florida and senior author of the study. “If chimaeras can make a set of teeth outside the mouth, where else might we find teeth?”

Fossil and modern evidence of tooth rods Researchers from the University of Washington and the University of Chicago examined both fossilized remains and living ghost sharks to unravel the mystery. One fossil, dating back 315 million years, revealed a tenaculum connected to the upper jaw that carried teeth strikingly similar to those found inside the mouth. Modern specimens taken from Puget Sound displayed the same head-based tooth development observed in the jaws of present-day sharks. Genetic analysis further confirmed that these structures activated the same genes responsible for producing oral teeth.

Juvenile Spotted Ratfish (Hydrolagus colliei) sits in the palm of the hand. Credit: Gareth J. Fraser, University of Florida

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“What we found is that the teeth on this strange appendage look very much like rows of shark teeth. The ability to make teeth transferred onto that appendage, likely from the mouth,” Fraser said. “Over time, the tenaculum shortened but retained the ability to make oral teeth on this forehead appendage.”

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

Distinguishing teeth from skin denticles Specialists in shark evolution and anatomy were fascinated by the tooth-covered rods emerging from the foreheads of ghost sharks. Their main question was whether the tenaculum contained genuine teeth connected to those in the mouth, or if it more closely resembled the tooth-like scales that cover the skin of sharks and some ghost sharks.

CT Scan of an Adult Male Spotted Ratfish Frontal Clasper

CT (computed tomography) scan of the adult male Spotted Ratfish frontal clasper (Tenaculum) covered in rows of teeth (rainbow colors). Credit: Specimen scanned by Karly Cohen; rendering and image by Ella Nicklin

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CT scans of the fossils and modern chimaeras gave the scientists unprecedented, detailed insights into the development of the tenaculum teeth, which looked remarkably similar to the teeth of today’s sharks. The nail in the coffin came from genetic evidence. The tenaculum teeth express genes found only in true teeth, never in shark skin denticles.

Evolutionary tinkering and surprising adaptation

“What I think is very neat about this project is that it provides a beautiful example of evolutionary tinkering or ‘bricolage,’” said Coates, a professor of biology at the University of Chicago. “We have a combination of experimental data with paleontological evidence to show how these fishes co-opted a preexisting program for manufacturing teeth to make a new device that is essential for reproduction.”

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

“The tenaculum is a developmental relic, not a bizarre one-off, and the first clear example of a toothed structure outside the jaw,” she said.

The bizarre path from a mouth full of teeth to forehead teeth used for mating demonstrates the impressive flexibility of evolution, the researchers say, always ready to repurpose structures for strange and unexpected new uses.

“There are still plenty of surprises down in the ocean depths that we have yet to uncover,” Fraser said.

Reference:

“Teeth outside the jaw: Evolution and development of the toothed head clasper in chimaeras”

by Karly E. Cohen, Michael I. Coates and Gareth J. Fraser, 4 September 2025, Proceedings of the National Academy of Sciences.

DOI: 10.1073/pnas.2508054122


TOPICS: Education; Outdoors; Pets/Animals; Weird Stuff
KEYWORDS: cryptobiology; ghostsharks; godsgravesglyphs; hickeys
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To: Red Badger
help males hold onto females

Sounds like a comparable tool could be made for humans.

It would be good to have something to steady all the bouncing around, which would keep the ashtray from falling off the back.

21 posted on 09/22/2025 7:41:30 AM PDT by fruser1
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To: fruser1

Or the beer from falling off the head...


22 posted on 09/22/2025 7:43:59 AM PDT by Sirius Lee ("Never argue with a fool, onlookers may not be able to tell the difference.”)
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To: Red Badger

Is that why they call you ‘Stubby”?


23 posted on 09/22/2025 8:00:03 AM PDT by null and void (The only man in all of Scotland is a 14 year old girl...)
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To: null and void

🙄😫😁...........................


24 posted on 09/22/2025 8:01:04 AM PDT by Red Badger (Homeless veterans camp in the streets while illegals are put up in 5 Star hotels....................)
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To: daniel1212

Right along the lines of theoretical physics.


25 posted on 09/22/2025 8:12:47 AM PDT by GMThrust
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To: null and void

Freud wept…


26 posted on 09/22/2025 8:51:10 AM PDT by Salamander (Please visit my profile page to help me go home again. https://www.givesendgo.com/GCRRD)
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To: dfwgator

That’s “frickin lasers.”


27 posted on 09/22/2025 4:27:43 PM PDT by EvilCapitalist (Pets are no substitute for children)
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To: PIF; Red Badger; SunkenCiv

My husband once caught a 3 foot sand shark at the NJ shore. We made 1 inch slices along the spine, and breaded and fried the pieces. I left a batch of the fried pieces in the refrigerator, and my little (7 and 10) sons would grab a piece whenever they were hungry and go back out to play. It was a tasty shark.


28 posted on 09/22/2025 5:48:49 PM PDT by gleeaikin (Question Authority: report facts, and post their links.is)
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To: gleeaikin

Rat fish are nothing like any variety of common shark

Shark, by the way is like deer meat, an incomplete protein - you need another protein source, like beans, to make a whole digestible protein - else the meal for nothing for you.


29 posted on 09/23/2025 4:47:30 AM PDT by PIF (They came for me and mine ... now its your turn)
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To: gleeaikin

I’ve tried shark, mostly for the irony, enjoyed it.


30 posted on 09/23/2025 6:31:11 AM PDT by SunkenCiv (NeverTrumpin' -- it's not just for DNC shills anymore -- oh, wait, yeah it is.)
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To: SunkenCiv

“”I’ve tried shark, mostly for the irony, enjoyed it.””

Tastes like chicken?


31 posted on 09/23/2025 6:32:35 AM PDT by Danie_2023
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To: Danie_2023

It’s got a tougher texture than most fish. Tastes okay. I’d much rather have swordfish or salmon.


32 posted on 09/23/2025 6:46:15 AM PDT by SunkenCiv (NeverTrumpin' -- it's not just for DNC shills anymore -- oh, wait, yeah it is.)
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To: PIF
Shark, by the way is like deer meat, an incomplete protein - you need another protein source

Somebody misinformed you. Both shark and venison are complete protein and very high protein per pound.

33 posted on 09/23/2025 7:02:28 AM PDT by ladyjane
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To: PIF
Shark, by the way is like deer meat, an incomplete protein

Nonsense

34 posted on 09/23/2025 7:04:45 AM PDT by Magnum44 (...against all enemies, foreign and domestic... )
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