Enamel makes up the visible part of the teeth and gives them their distinctive appearance. However, researchers have now found that enamel did not evolve in the mouth but in the skin of ancient fish. (Photograph: Antonio Guillem/Shutterstock)

Oct 12, 2015 | News Nordic

UPPSALA, Sweden: Tooth enamel is the hardest substance produced by the human body. Since enamel is one of the four major tissues that make up the teeth and gives them their distinctive shiny white appearance, it comes as a surprise that a study has found that enamel most likely originated from an entirely different part of the body: the skin.

Unlike humans, who only have teeth in the mouth, certain fish species have little tooth-like scales on the outer surface of the body. In the study, researchers from Uppsala University in Sweden and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing in China analysed Lepisosteus, an ancient gar fish from North America whose scales are covered with an enamel-like tissue called ganoine. 

They found genes for two of the three unique matrix proteins of enamel expressed in the genes of Lepisosteus’s skin, and this strongly suggests that ganoine is a form of enamel. In order to determine where the enamel first originated—the mouth or the skin—the researchers then investigated the dermal denticles on two fossil fishes: Psarolepis from China and Andreolepisfrom Sweden. 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 bear enamel. 

Their findings suggest that enamel in fact first evolved in the skin. Dr Per Ahlberg, Professor of Evolutionary Organismal Biology at Uppsala University, explained: “Psarolepis and Andreolepisare among the earliest bony fishes, so we believe that their lack of tooth enamel is primitive and not a specialisation. It seems that enamel originated in the skin, where we call it ganoine, and only colonised the teeth at a later point.”

The study is the first to combine novel palaeontological and genomic data in a single analysis to explore tissue evolution. The results have been published online on 23 September in theNature journal in an article titled “New genomic and fossil data illuminate the origin of enamel”
From http://www.dental-tribune.com