If you’ve ever flinched during a cold drink or a dental cleaning, you know that our teeth can be incredibly sensitive.
That sensitivity is thanks to a tissue called dentine, which lies beneath the hard enamel and connects to the nerves inside each tooth.
It helps us feel things like temperature, pressure, and pain when we eat and drink.
But dentine didn’t originally evolve for chewing or dental pain. According to a new study from the University of Chicago, dentine first developed in ancient armored fish—not in their mouths, but in the hard plates covering their bodies.
These plates had tiny bumps called odontodes, and the dentine inside them acted like a sensor, helping the fish sense movement and changes in the water around them.
This discovery came about when Yara Haridy, a postdoctoral researcher in Neil Shubin’s lab, was looking for the oldest vertebrate (or backbone-having) animal in the fossil record.
She collected hundreds of ancient fossil fragments from museums and scanned them using a high-powered particle accelerator at Argonne National Laboratory to look for signs of dentine.
At first, Haridy and her team thought they had found dentine in a fossil called Anatolepis, which would have made it the oldest known vertebrate. They were thrilled—thinking they had found the first tooth-like structure in the fossil record.
But after comparing it to modern crabs and other ancient fossils, they realized it wasn’t dentine after all. It was something called sensilla—tiny sensory organs found on the shells of arthropods like crabs and shrimp.
This led them to a surprising conclusion: these tooth-like structures in both fish and invertebrates may have evolved independently to help animals sense their environment.
In some armored fish like Eriptychius, the researchers did confirm real dentine in structures similar to those in arthropods—suggesting that teeth may have evolved from these sensory bumps on the skin, not the other way around.
Today, some modern fish like sharks and catfish still have these dentine-covered bumps on their skin, called denticles. Haridy found that these, too, are connected to nerves, just like our teeth.
The findings support a theory called the “outside-in” hypothesis, which suggests that sensory structures first evolved on the outside of animals and were later adapted into teeth inside the mouth.
While the researchers didn’t find the oldest vertebrate after all, Shubin said they discovered something even more exciting: a deeper understanding of how animals first began to sense the world around them—and how our tooth sensitivity has ancient roots in armored fish.
