A new study suggests that your toothache might trace its roots back to a 500-million-year-old fish. Teeth, it turns out, didn’t start out in the mouth for chewing. Instead, their earliest evolutionary ancestors tiny structures called odontodes first appeared on the outer armor of some of the planet’s earliest fish and were likely used for sensing the environment, according to findings published in the journal Nature.
These hard structures, odontodes, predate jaws and were scattered across ancient fish exoskeletons. Today, they persist in the form of tiny “skin teeth” that roughen the hides of modern sharks, stingrays, and catfish. Long thought to serve a range of functions from predator protection to hydrodynamics the new research supports the idea that their original role was sensory.
The study was led by Yara Haridy, a postdoctoral researcher at the University of Chicago, who stumbled upon the breakthrough while scanning ancient fossils with a CT machine to investigate early vertebrates. A fossil from the Cambrian period, Anatolepis, initially thought to be the oldest known vertebrate, turned out to share more in common with invertebrate arthropods like crabs and spiders, specifically the sensory organs known as sensilla. These structures allow arthropods to detect temperature, vibrations, and smells and they appear almost unchanged over half a billion years.
When Haridy compared these ancient features to those found in 465-million-year-old fish fossils, she and her team noticed remarkable similarities. Modern fish also helped confirm the theory. Experiments on catfish, sharks, and skates showed nerves present in their external “teeth,” confirming that odontodes outside the mouth can still relay sensory information.
“Arthropods and early vertebrates independently evolved similar sensory solutions to the same biological and ecological problem,” said Haridy.
Senior study author Neil Shubin noted that these evolutionary adaptations emerged in “a pretty intense predatory environment,” where sensing water pressure and movement was likely key to survival.
Eventually, as jaws evolved, these sensory odontodes migrated toward and into the mouth, where their hard, pointed form became useful for grasping and chewing leading to the teeth we know (and suffer from) today.
So next time your teeth ache from ice cream or a dental visit, remember it may be the echo of a half-billion-year-old survival tool inherited from armored, jawless fish navigating ancient seas.