We humans possess a thin coating of enamel -- the hardest tissue produced in the body -- on our teeth that protects from everyday chewing, biting crunching and grinding. But where did this substance originate?

That was the question researchers from Uppsala University and the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) attempted to answer recently in examining gar fish and ancient fish fossils. Their conclusion was that enamel got its start in the scales of ancient fish.

Humans only have teeth in their mouths, but certain fish have "dermal denticles," meaning they have tooth-like scales on the outside of their body. A living example of this are North American gar fish (Lepisosteus) whose scales are covered with an enamel-like tissue called "ganoine."

After analyzing the fish's DNA, Tatjana Haitina, a researcher at the Department of Organismal Biology at Uppsala University, discovered that enamel genes were expressed in its skin. This indicates that ganoine is a form of enamel (read news release here).

Two 400 million-year-old fossil fishes, Psarolepis from China and Andreolepis from Sweden, were also examined for this study. The researchers discovered that the scales and denticles of Psarolepis were covered in enamel, but its teeth were not. On the other hand, in Andreolepis, only the scales were composed of enamel.

"Psarolepis and Andreolepis are among the earliest bony fishes, so we believe that their lack of tooth enamel is primitive and not a specialization. It seems that enamel originated in the skin, where we call it ganoine, and only colonized the teeth at a later point," Per Ahlberg, a professor of evolutionary organismal biology at Uppsala University, said in a statement.

Their findings were recently published in the journal Nature

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