The connection between our teeth and the scales of a fish

About the episode

Humans aren’t usually associated with scales, but we need to start thinking differently, a teeth study has found.

How did the teeth form? Teeth that ensured that as an animal you could suddenly grab prey or plants better and could also tear them to pieces more easily. According to the researchers, it all started with a species of fish. The ancestor of all toothed animals.

But even then: how did these teeth come about? According to one theory, the scales on the outside of the fish migrated to the inside of the mouth. Another sees it upside down: just like gill tissue, teeth must have developed from within.

This new study looked at sawfish to clarify which theory fits best. Researchers studied 70 million year old fossils of an extinct species of sawfish. Specifically, they looked at the sharp protrusions on the animal’s nose, which is why the word saw appears in the name. These pointed protrusions are often called teeth, but are actually specialized scales.

When they examined the structure of the outer layer of these scales under the microscope, they were surprised to see that this structure is quite similar to modern shark teeth. Swordfish also had real teeth in addition to these scales, so they did not change places in this animal, but it shows that scale-like structures can easily develop into tooth-like structures. A plus for the “outside in” theory. Think about that the next time you scrub your scales.

Read more: Sawfish fossils suggest teeth likely evolved from the body scales of ancient fish.