About the episode
Humans aren’t generally associated with scales, but we need to start thinking differently, according to a study on teeth.
How did teeth ever form? Teeth that ensured that as an animal you could suddenly grip prey or plants better and that you could also tear them apart more easily. According to the researchers, it all started with one kind of fish. The ancestor of all animals with teeth.
But even then: how did those teeth ever come in? According to one theory, the scales on the outside of the fish migrated inside the mouth. Another sees it the other way around: Just like gill tissue, teeth must have grown from within.
This new study looked at sawfish to clarify which theory fits best. Researchers studied 70-million-year-old fossils of an extinct sawfish species. Specifically, they observed the sharp protrusions on the animal’s nose, which is why the word saw appears in the name. Those pointed protrusions are often referred to as teeth, but they’re actually specialized scales.
When they looked at the structure of the outer layer of these scales under a microscope, they were surprised to see that this structure is quite similar to modern shark teeth. Swordfish also have true teeth in addition to these scales, so they have not changed places in this animal, but it does show that scale-like structures can easily develop into tooth-like structures. A plus for the “outside-in” theory. Think about that next time you cleanse scales.
Read more: Sawfish fossils suggest that teeth likely evolved from body scales in ancient fish.
