Teeth are good for chewing and biting, but they are also sensitive – and that may have been their original function hundreds of millions of years ago
By Michael Marshall
21 May 2025
CT scan of the front of a skate, showing the hard, tooth-like denticles (orange) on its skin
Yara Haridy
Teeth first evolved as sensory organs, not for chewing, according to a new analysis of animal fossils. The first tooth-like structures seem to have been sensitive nodules on the skin of early fish that could detect changes in the surrounding water.
The finding supports a long-standing idea that teeth first evolved outside the mouth, says Yara Haridy at the University of Chicago.
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While there was some evidence to back this up, there was an obvious question. “What good is having all these teeth on the outside?” says Haridy. One possibility was that they served as defensive armour, but Haridy thinks there was more to it. “It’s great to cover yourself in hard things, but what if those hard things could also help you sense your environment?”
True teeth are only found in backboned vertebrates, like fish and mammals. Some invertebrates have tooth-like structures, but the underlying tissues are completely different. This means teeth originated during the evolution of the earliest vertebrates: fish.
Haridy and her team re-examined fossils that have been claimed to be the oldest examples of fish teeth, using a synchrotron to scan them in unprecedented detail.