Teeth are some of the most sensitive parts of the body, giving us important signals about temperature, pressure, and pain when we eat.
But new research shows that teeth weren’t always used for chewing—in fact, they may have started out as sensory tools embedded in the armored skin of ancient fish.
In a study led by scientists from the University of Chicago and published in Nature, researchers discovered that dentin—the sensitive inner layer of modern teeth—first evolved as a sensory material in the bumpy armor of early fish.
These armored structures, called odontodes, date back to around 465 million years ago and likely helped fish detect movement and pressure in the water around them, rather than chew food.
Paleontologists have long debated how teeth evolved, with many pointing to these ancient armor bumps as the starting point.
But until now, their function was unclear. Using ultra-detailed CT scans, the researchers found evidence of dentin inside these structures in a fossil fish called Eriptychius. This confirms that the sensory capability of teeth existed long before mouths were filled with them.
The project began when lead author Dr. Yara Haridy was looking for signs of the earliest vertebrate animals in the fossil record.
She gathered hundreds of fossil samples from museums across the country, some small enough to fit on a toothpick, and scanned them at the Advanced Photon Source at Argonne National Laboratory.
One fossil from a Cambrian-period creature called Anatolepis seemed to show dentin, suggesting it could be the earliest vertebrate. The team was thrilled—until they compared the structure with those found in arthropods like crabs and shrimp.
What looked like vertebrate dentin turned out to be very similar to sensilla—tiny sensory organs found in the shells of modern arthropods. That meant Anatolepis wasn’t a vertebrate fish at all, but an invertebrate with armor that served a similar purpose.
This discovery helped resolve confusion over several ancient fossils and revealed that both vertebrates and invertebrates developed similar sensory structures independently.
The researchers then confirmed their findings by looking at modern species like crabs, catfish, sharks, and skates. The tooth-like denticles on catfish skin, for example, were connected to nerves and functioned much like teeth. This further supports the idea that sensory armor existed before actual teeth.
These findings strengthen the “outside-in” theory of tooth evolution. Rather than starting inside the mouth and spreading outward, teeth likely evolved from sensory structures on the outside of the body. Over time, animals adapted the same genetic tools to grow these sensitive structures inside their mouths for eating.
Though the team didn’t find the earliest vertebrate as they’d hoped, they made a surprising and exciting discovery. “We didn’t find the earliest one, but in some ways, we found something way cooler,” said senior author Dr. Neil Shubin.
The study sheds new light on how animals first began sensing the world around them and reveals that long before teeth were used for biting, they were used for feeling.
