Tooth Enamel Originated In Our Skin?

How did our teeth enamel evolve? And where did the tissue first appear?

New findings published in the journal Nature reveal that our enamel originated in the skin and that our teeth colonized much later, according to researchers from the Institute of Vertebrate Paleontology and Palaeoanthropology (IVPP) in Beijing, China.

Of course, most of us know what our teeth enamel is. It's the shiny stuff coated on our teeth and it's also the hardest substance produced by the body that's composed almost entirely of the mineral apatite (calcium phosphate) deposited on a substrate of three unique enamel matrix proteins.

Though we only have this shiny, hard stuff in our mouths, certain sharks have "dermal denticles," including tooth-like scales on the outer surface of the body. In fact, many fossil bony fish and even a few archaic living ones as the gar from North America have scales that are covered with an enamel-like tissue called "ganoine."

In this recent study, researchers at the Department of Organismal Biology, Uppsala University, investigated the genome of Lepisosteus, which was sequenced by the Broad Institute. They discovered that it contains genes for two or our three enamel matrix proteins. Researchers identified the first from a ray-finned bony fish. The other genes were expressed in the skin, strongly suggesting that ganoine is a form of enamel.

Yet just where did our tooth enamel come from? The skin? The mouth? Both? They found that two fossils provided the answer: Psarolepis from China and Andreolepis from Sweden, which are both more than 400 million years. In Psarolepis the scales and the denticles of the face are covered with enamel, but there is no enamel on the teeth; in Andreolepis only the scales carry enamel, according to researchers Qingming Qu and Per Ahlberg of Uppsala University in collaboration with Min Zhu from IVPP in Beijing.

"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," concluded Per Ahlberg, Professor of Evolutionary Organismal Biology at Uppsala University, in a news release.

Future studies will further explore the evolution of vertebrate hard tissues.

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