Your Tooth Enamel Might Have Started As Fish Scales

SCIENCE

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Discussion Ideas

The Popular Science article says enamel is only found in vertebrate teeth. Do invertebrates even have teeth?
- No. True teeth are only found in vertebrates. Teeth are hard, bone-like structures that are attached, usually in a row or rows, to a vertebrate’s jaw.
- Many invertebrates have structures similar to teeth.
  - Mollusks such as limpets, for instance, have a tongue-like, ribbon-like organ called a radula that is barbed with more than a thousand tooth-like structures.
  - Arachnids such as funnel-web spiders have complex mouthparts called chelicera that act as “fangs.”

New research tested scales from both fossils and extant fish with ganoid scales, and compared the scales’ proteins to proteins found in tooth enamel. What are ganoid scales?
- Ganoid scales, one of four major types of fish scales, contain the mineral ganoine. They are hard, solid, diamond-shaped scales found on ancient, weird-looking fishes such as gar, sturgeon, and paddlefish.

So, how did ganoid fish scales become tooth enamel?
- They didn’t! (Evolution doesn’t work like that.) Research shows that ganoid scales contain enamel matrix proteins and other chemicals linked to enamel development in teeth. So, a better question is: How did proteins get from scales to teeth? Follow the ganoine:
  - Some of the very earliest bony fishes had ganoid scales, but no tooth enamel—their teeth were “naked dentine.”
  - “Somewhere along the evolutionary line, some of these ancient fish began to incorporate ganoine/enamel into other hard surfaces of their bodies, eventually … evolving with ganoine/enamel on their actual teeth, a trait that has been passed down the evolutionary line to almost all toothed creatures today, from humans to crocodiles.”

TEACHERS TOOLKIT

Nat Geo: Clue to a People’s Origins video

Australian Museum: Fish Scales

National Geographic Education Blog