Anyone who has ever squirmed through a dental cleaning can tell you how sensitive teeth can be. This sensitivity gives important feedback about temperature, pressure—and yes, pain—as we bite and chew our food. However, the sensitive parts inside the hard enamel first evolved for something quite different.
New research from the University of Chicago shows that dentine, the inner layer of teeth that transmits sensory information to nerves inside the pulp, first evolved as sensory tissue in the armored exoskeletons of ancient fish.
Paleontologists have long believed that teeth evolved from the bumpy structures on this armor, but their purpose wasn’t clear. The new study, published this week in Nature, confirms that these structures in an early vertebrate fish from the Ordovician period about 465 million years ago contained dentine, and likely helped the creature sense conditions in the water around it.
The research also showed that structures considered to be teeth in fossils from the Cambrian period (485-540 million years ago) were similar to features in the armor of fossil invertebrates, as well as the sensory organs in the shells of modern arthropods like crabs and shrimp. These similarities imply that sensory organs in the armor of diverse animals evolved separately in both vertebrates and invertebrates to help them sense the larger world around them.
Toothache from eating something cold? Blame these ancient fish
“When you think about an early animal like this, swimming around with armor on it, it needs to sense the world. This was a pretty intense predatory environment and being able to sense the properties of the water around them would have been very important,” said Neil Shubin, PhD, Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy at UChicago and senior author of the new study. “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.”
Night at the particle accelerator
Yara Haridy, PhD, a postdoctoral researcher in Shubin’s lab who led the study, wasn’t looking for the origins of teeth when she started the project. Instead, she was hoping to answer another longstanding paleontological question: What is the earliest vertebrate in the fossil record? Haridy asked museums around the country for fossil specimens from the Cambrian period (485-540 million years ago) so she could CT scan them, looking for telltale signs of vertebrate features.
Read the full story by Matt Wood, originally published May 21, 2025