Have you ever bitten into ice cream and felt like a tiny lightning bolt struck inside your mouth? That sharp jolt of pain isn’t without reason.
Surprisingly, the pain caused by tooth sensitivity we experience today has incredibly ancient roots—dating back some 465 million years. And it all began with ancient fish whose bodies were covered in tiny, tooth-like structures embedded in their skin.
Yes, you read that right. Before teeth were used for chewing as they are now, they served a completely different purpose: as sensory tools.
A recent study published in the scientific journal Nature reveals that our teeth, sensitivity and all, may have originated from primitive structures called odontodes, which, interestingly, were not located inside the mouth at all.
The Origin of Teeth: Not for Chewing
Before teeth evolved for chewing, they had a very different function: sensing the environment. For years, scientists have been trying to answer one major question: Where did teeth actually come from?
The key clue lies in tooth-like structures found in the skin of ancient fish. These structures, known as odontodes, are essentially small, hard bumps resembling teeth that were embedded in the skin. They weren’t part of the mouth, they acted as a protective outer layer, like armor.
But recent research uncovered something even more fascinating: these odontodes were sensitive to environmental stimuli. They weren’t just a shield; they were also sensory tools. They helped ancient animals sense their surroundings, such as changes in water pressure, temperature, or movement from nearby creatures.
A Half-Billion-Year-Old Sensation
The new study, published in Nature, reveals that ancient odontodes already contained dentin, the same inner layer of modern teeth responsible for transmitting pain signals to nerves. Today, this dentin is what reacts when we bite into something very cold, sweet, or hard.
But in ancient times, dentin wasn’t in the mouth. It was embedded in the "skin" of prehistoric fish. This means its original purpose wasn’t to chew, but to feel the world: sensing pressure, temperature, and possibly detecting threats.
Uncovering Microfossils from the Distant Past
This groundbreaking research was led by Dr. Yara Haridy, a postdoctoral researcher at the University of Chicago. Initially, her goal wasn’t to study teeth, she aimed to identify the oldest known vertebrates from the Cambrian period, which dates back roughly 540 to 485 million years ago. She collected hundreds of microfossils, including one intriguing specimen known as Anatolepis.
For years, Anatolepis was believed to be one of the earliest vertebrate fish because its body was covered in tooth-like bumps. However, high-resolution CT scans revealed a surprising twist: the bumps resembled sensilla, sensory organs typical of invertebrates like crabs and shrimp, more than true tooth structures.
This led to a startling conclusion: Anatolepis was not a fish at all, but an ancient arthropod. The discovery has significantly revised a long-standing scientific belief.
Sensilla and Odontodes: A Remarkable Case of Evolution
This finding points to a profound insight: both vertebrates (like early fish) and invertebrates (such as arthropods like shrimp and crabs) independently developed very similar sensory structures. This phenomenon is known as evolutionary convergence, when unrelated species evolve similar solutions to cope with the same environmental challenges.
In invertebrates like shrimp, the structures are called sensilla, while in early fish, they are known as odontodes. Though they stem from different evolutionary origins, both structures highlight one key survival strategy in a dangerous world: the ability to sense the surrounding environment.
From Sensors to Chewing Tools
Over time, ancient fish evolved jaws, and odontodes began to appear near the mouth. Gradually, these structures migrated into the mouth and transformed into teeth—but their sensory function remained.
The dentin layer beneath our tooth enamel still contains nerves. That’s why teeth can feel pain when exposed to extreme stimuli like cold or sugar. In other words, the sharp sting of a sensitive tooth is a leftover legacy of an ancient sensory system that once helped creatures sense the world around them.
