Fossil discovery explains why our teeth are still so sensitive to cold

For most of us, teeth mean crunching pretzels or tearing steak. But a new fossil analysis suggests their first job was feeling the world, not shredding it.

“What good is having all these teeth on the outside?” asked Yara Haridy of the University of Chicago, lead author of the study. Using high‑energy scans, researchers found that the earliest tooth‑like bumps sat on fish skin and were wired for sensation. 

Teeth began as skin sensors

These skin teeth, known as odontode units, appear in Eriptychius fossils from the middle Ordovician Period, roughly 460 million years ago.

Slicing the fossils reveals thick bands of dentine, the same pain‑transmitting material that still lies beneath human enamel.

Each odontode contains a pulp cavity and wide tubules that open at the surface, a layout ideal for detecting pressure or temperature shifts. By contrast, later fish with heavy enamel caps muted that sensitivity but gained better protection.

One celebrated Cambrian candidate for the “first fish,” Anatolepis, has been demoted after fresh scans showed its bumps match arthropod sensilla, not vertebrate dentine.

Early armor came with nerves

Sensilla in crabs and scorpions let them taste, feel vibration, and track currents. Early vertebrates adopted a similar strategy, embedding nerves inside mineral caps that hardened into armor.

“Tooth‑like structures likely first evolved in the skin of early vertebrates, prior to the oral invasion of these structures that became teeth,” said Gareth Fraser of the University of Florida, an evolutionary biologist not involved in the scans.

Because armor muffles most tactile cues, adding built‑in sensors restored environmental awareness without sacrificing defense. The same compromise appears again and again whenever animals grow shells, scales, or plates.

The Ordovician seas teemed with cephalopods and sea scorpions, so feeling a predator brush past could mark the difference between survival and lunch. Even a thin sensory layer offered that edge.

Teeth moved from skin to mouth

Once fish started lunging at prey, bringing those hard nodules inside the oral cavity made practical sense. The genetic toolkit for building odontodes simply redeployed along the jaw line.

CT reconstructions show a stepwise shift, first lining lips, then clustering on internal ridges that became true teeth. No new tissue was required, only a new address.

This migration explains why modern teeth still flinch when chilled soda hits exposed dentine. The tissue did not lose its ancient job, even after millions of years chewing.

Human odontoblast cells inside dentine express temperature‑sensing TRP channels that trigger pain signals, reinforcing the link between sensation and tooth structure.

Ice cream pain is ancient

Skates, sharks, and certain catfish still wear odontodes across their skin, and fluorescent imaging reveals nerves curling around each unit. The same wiring lights up in their oral teeth.

Dentists encounter the legacy daily: about 30 percent of adults report dentin hypersensitivity – a direct outcome of open tubules harking back to those armored swimmers.

Laboratory studies show that activating TRPA1 and TRPV4 channels in human odontoblasts releases ATP, a chemical that excites nearby nerves and sparks the familiar zing of ice‑cream pain.

Understanding the fossil record clarifies why blocking tubules with varnishes or bioactive glasses calms sensitivity more reliably than numbing gels alone. Closing the ancient sensory windows cuts the signal at its source.

Fossil mistake changed tooth history

The misidentification of Anatolepis as a vertebrate with dentine pushed the timeline of true teeth further back than the evidence supports.

With updated scans showing Anatolepis as an arthropod, the emergence of real vertebrate dental tissue now firmly begins in the middle Ordovician.

This correction removes about 40 million years of assumed vertebrate history. It also reorients where scientists search for the evolutionary leap from external skin sensors to internal biting tools.

Ancient teeth link to modern health

Reclassifying Anatolepis as an arthropod pushes the oldest confirmed vertebrate dentine forward by almost 40 million years, tightening the evolutionary timeline. Paleontologists can now focus on Ordovician strata when hunting the first mouths with teeth.

The fossil findings also challenge textbook diagrams that present teeth as novel structures formed deep inside the jaw.

Instead, they appear as immigrants from the skin, carrying sensory baggage that still shapes dental health.

Medical researchers already mine shark and skate genes to inspire regenerative dentistry. Knowing those genes once built skin sensors may guide efforts to coax human cells into growing replacement enamel.

Finally, the study highlights a broader pattern: nature often solves different problems with the same parts.

Sensory armor, lateral‑line canals, and even mammal whiskers show how sensation sneaks into protective structures whenever the need arises.

The study is published in Nature.

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