Unlocking the Secrets of Tooth Pain: What a 465-Million-Year-Old Armored Fish Can Teach Us

Ever wonder why our teeth hurt? It turns out, the answer goes back millions of years to ancient fish.

Our teeth have two main layers. The hard outer layer, called enamel, protects the inner layer known as dentine. Dentine is what causes pain when we bite something hard or feel the chill of ice cream.

For a long time, scientists debated the origins of teeth. A new study sheds light on this mystery, suggesting teeth evolved from tiny bumps on fish. These bumps, called odontodes, were once puzzling to researchers.

Recent findings show that in a fish from the Ordovician period—around 465 million years ago—these bumps contained dentine. Using 3D scans of fossils, scientists discovered that these structures weren’t just for show. They likely helped ancient fish sense their environment, picking up changes in temperature or pressure around them.

Interestingly, the odontodes resemble sensilla, which are tiny sensory organs found in crabs and shrimp, as well as ancient invertebrates. Despite being different types of animals, both fish and arthropods developed these similar features independently, a phenomenon called evolutionary convergence. Dr. Yara Haridy, who led the research, highlights this remarkable similarity. “We know that vertebrates and arthropods evolved hard parts independently,” she explains.

For years, scientists thought a Cambrian-era fossil named Anatolepis was one of the earliest vertebrates due to its tooth-like bumps. However, close examination using high-resolution CT scans revealed that these bumps didn’t have dentine. They were more like the sensory structures found in arthropods. This means Anatolepis was likely an ancient arthropod, not a vertebrate.

These findings underscore the shared evolutionary paths of creatures with backbones and those without. Both groups created ways to sense their surroundings using nerve-connected structures within hard outer shells, whether from fish skin or crab shells.

The researchers also looked at modern examples, such as suckermouth catfish. These fish have small tooth-like scales, or denticles, on their skin that are directly connected to nerves. “We think that the earliest vertebrates had very similar structures,” Dr. Haridy notes.

This research supports a key theory in evolution—the "outside-in" hypothesis—which suggests teeth evolved from sensory structures. Long before animals developed mouths full of teeth, their sensitive armor helped them navigate their environments.

Neil Shubin, the senior author of the study, remarked, “We didn’t find the earliest vertebrate, but in some ways, we found something way cooler.”

This work was published in the journal Nature. It encourages us to rethink what we know about the evolution of teeth and sensory structures in our ancient ancestors.

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