Scientists at the University of Chicago have discovered that the sensitive tissue inside our teeth first evolved as part of the armored skin of ancient fish. Their new study, published in Nature, confirms that dentine—a key part of teeth—was originally used by early vertebrates to sense their surroundings.
This research supports the idea that dentine wasn’t always used for chewing. Instead, millions of years ago, it helped fish detect changes in the water. The study also clears up confusion about Anatolepis heintzi, a fossil once thought to be the earliest known vertebrate because of its dentine-like structures.
For years, scientists debated whether Anatolepis was really an early vertebrate. The fossil had tiny tubules that some researchers believed were odontodes—small structures considered to be the ancestors of teeth. However, there wasn’t enough evidence to be sure.
To settle the debate, scientists used synchrotron scanning, a powerful imaging technique, to study different fossils and modern creatures. The scans revealed that Anatolepis didn’t have dentine. Instead, its tubules were sensory structures similar to those found in arthropods like crabs and shrimp. These structures, called sensilla, help animals detect their surroundings.
“This shows us that ‘teeth’ can also be sensory even when they’re not in the mouth,” said lead researcher Yara Haridy, PhD. “There’s sensitive armor in these fish. There’s sensitive armor in these arthropods. This explains the confusion with these early Cambrian animals.”
Although Anatolepis turned out to be an arthropod, researchers did find real dentine in another ancient fish. The Ordovician vertebrate Eriptychius, which lived about 465 million years ago, had large dentine-filled tubules in its armor. This confirms that dentine first evolved in vertebrates as a sensory tissue.
Further tests showed that modern fish, such as sharks and teleosts, still have nerve connections in their external dentine structures. This means early vertebrates may have used dentine to sense their environment before it became part of teeth.
Scientists have two main ideas about how teeth came to be. The “inside-out” theory suggests teeth evolved first and were later adapted for exoskeletons. The new research supports the “outside-in” theory, which argues that sensory structures appeared first in exoskeletons and later evolved into teeth.
While the team didn’t find the oldest vertebrate fish, study co-author Neil Shubin, PhD, believes the discovery is still important. “We didn’t find the earliest one, but in some ways, we found something way cooler,” he said.
Source: University of Chicago, Nature
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