Yara Haridy, a postdoctoral researcher at the University of Chicago, was originally searching for the oldest fossil of an animal with a backbone—paleontology is, after all, her field. But her research led to a surprising finding: insights into the origin of teeth.
In a study recently published in Nature, Haridy—who led the research in Neil Shubin’s lab—found that the sensitive interior of human teeth may have evolved from sensory tissue in the armored exoskeletons of ancient fish that swam Earth’s oceans during the Cambrian period, about 485 to 540 million years ago.
“This was a pretty intense predatory environment, and being able to sense the properties of the water around them would have been very important.” Dr. Neil Shubin, senior author of the study.
The inner layer of a tooth, known as dentine, carries sensory information—like the sharp jolt you feel when sipping something very hot or cold—through tiny tubules that connect to nerves.
“When you think about an early animal like this, swimming around with armor on it, it needs to sense the world,” said said Neil Shubin, PhD, Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy at UChicago and senior author of the new study. “This was a pretty intense predatory environment, and being able to sense the properties of the water around them would have been very important. So here we see that invertebrates with armor, like horseshoe crabs, need to sense the world too—and it just so happens they hit on the same solution.”
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“This shows us that ‘teeth’ can also be sensory even when they’re not in the mouth.” Dr. Yara Haridy, who led the research.
So how is it possible that modern tooth sensitivity can be traced back to ancient fish armor?
What Haridy and the team confirmed is that dentine first evolved as sensory tissue in the armor of these long-extinct fish. Paleontologists have long believed that teeth evolved from the bumpy structures on these exoskeletons.
To explore this, Haridy used a CT scanner to analyze hundreds of fossil specimens from museums across the United States. But when she compared one particular fossil to others she had scanned, she noticed something unusual: the tubules in the structure looked more like sensilla, the sensory organs found in arthropods such as crustaceans and insects.
This surprising twist led to the reclassification of the fossil creature Anatolepis—once thought to be the oldest vertebrate. It turns out it wasn’t a vertebrate at all, but an arthropod.
“This shows us that ‘teeth’ can also be sensory even when they’re not in the mouth,” Haridy said. “There’s sensitive armor in these fish. There’s sensitive armor in arthropods. This helps explain the confusion with these early Cambrian animals. People thought Anatolepis was the earliest vertebrate—but it actually was an arthropod.”