Bizarre new research suggests enamel originated in the skin before eventually colonizing in the teeth.
The recent study was the first to combine novel palaeontological and genomic data to perform an analysis of tissue evolution, Uppsala University reported.
Enamel is the hardest substance produces by the body, and is composed almost entirely of the mineral apatite. Humans only have this shiny white substance on their teeth, but certain types of fish and sharks have "dermal denticles," or tooth scales, on their bodies. Many fossil fish, and a few modern ones, have scales covered in enamel-like tissue called "ganoine."
To make their findings, a team of researchers sequenced the genome of the gar (Lepisosteus), and found it contained the contains genes for two of our three enamel matrix proteins, which are the first of their kind to be identified in bony fish. These genes were strongly expressed in the skin, which could mean ganoine is actually a type of enamel.
Wondering where in the body enamel originated, the researchers looked at the 400 million-year old fossil fish Psarolepis from China and Andreolepis from Sweden. The scales and facial denticles of Psarolepis are coated in enamel, but oddly enough the ancient fish did not have enamel on their teeth. Traces of enamel were only found in the scales of the Andreolepis.
"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," said Per Ahlberg, Professor of Evolutionary Organismal Biology at Uppsala University.
The findings were published in a recent edition of the journal Nature.
