Tooth enamel origin unearthed

In a study published in the latest edition of the widely read science journal Nature, researchers representing Beijing, China’s Institute of Vertebrate Palaeontology and Palaeoanthropology or IVPP and Sweden’s Uppsala University have combined data from two different fields of research, genomics and paleontology. They have combined the data for finding an accurate answer to the question: “did enamel originate in the skin and then colonized the teeth”.

For those who don’t know: Enamel is the hard, glossy substance that create the covering of the crown of a tooth. Enamel is the reason why we see our teeth gleaming back at us when we brush them standing in front of the bathroom mirror every morning. According to experts, it is the hardest substance produced naturally by the body.

Enamel, almost entirely, is made of a mineral called apatite, which is calcium phosphate. To form enamel, apatite gets deposited on a unique substrate composed of 3 enamel matrix proteins.

Humans, like all other land vertebrates, have teeth only inside their oral cavity. However, some fishes, for instance, sharks other than having teeth in their mouth, also possess structures known as “dermal denticles” on the outer surface of their body. The dermal denticles are teeth-like scales.

Scientists have found that in fossils of several bony fishes as well as in some archaic living ones like Lepisosteus or gar found in North America, scales carry a covering of ganoine, a tissue with properties similar to that of enamel.

Tatjana Haitina of the Uppsala University examined Lepisosteus’ genome and came to know that it carries genes for 2 out of the 3 enamel matrix proteins we have. What’s even more fascinating is that these genes get expressed in the fish’s skin, which clearly indicates that ganoine is nothing but a kind of enamel.

This gives birth to a fresh question: “where did the tissue called enamel originate, on the skin, in the mouth or in both places”. This question has been aptly answered by a couple of fossil fishes, Sweden’s Andreolepis and China’s Psarolepis. Both these fossil fishes used to live over 400 million years back.

Scientists studying the fossils of these fishes revealed that the scales and denticles in the face of Psarolepis used to have an enamel covering. However, their teeth weren’t covered by enamel. In case of Andreolepis, it was found that only their scales carried enamel.

According to Uppsala University’s Prof. Per Ahlberg, Andreolepis and Psarolepis are two of the most ancient bony fishes. As a result, the research team conducting the study believes that not having tooth enamel is not any specialization, but the proof of the fact that the species are primitive. Prof. Ahlberg added that it appears that enamel has its origin in the skin, where it’s called ganoine, and it colonized teeth of vertebrates much later.