Enamel evolved in fish skin, according to reports in ScienceDaily 23 September 2015. Enamel is the hardest substance found in living organisms. It consists of a mineral calcium hydroxyapatite, which is laid down in a matrix of three proteins that are unique to enamel. In a search for the origin of enamel, scientists from Uppsala University in Sweden and the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) in Beijing, China have studied fish fossils and fish genetics.
Enamel is found in the teeth of some lobe finned fish, but not in most bony fish, and it was assumed that these fish cannot produce enamel. The researchers studied fossils of an extinct bony fish called Psarolepis romeri and found it had enamel in its scales and its skull, but not in its teeth. Another extinct fish Andreolepis was found to have enamel in its scales. Both of these fish are dated as over 400 million years old.
The team then studied the genome of a living bony fish, the spotted gar (Lepisosteus oculatus), which has scales covered in a hard substance named ganoine. They found this fish has genes for two of the proteins in the matrix involved in enamel formation, but these are only expressed in the skin, and not in the teeth.
The researchers concluded that ganoine is a form of enamel, and enamel originally evolved in skin enamel then migrated to the teeth via the skull. Per Ahlberg, Professor of Evolutionary Organismal Biology at Uppsala University explained: “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”.
Editorial Comment: This study may explain why two extinct fish and the living spotted gar fish have hard scales, but it does not explain where such enamel came from. The gar fish already has the fully functioning genes needed to make ganoine, and it is reasonable to assume that the Psarolepis and Andreolepis had them as well.
This study does remind us of an important aspect of genetics – it’s not just about having genes that produce substances, e.g. enamel matrix proteins, but also needed is a mechanism to switch such genes off and on in the right locations, since the genes exist in every cell, but they are only needed in a few cells. Such control information is just as important as the substance information, and it reminds us that there needed to be a bigger picture at work concerning how the whole creature is formed and functioned so that right genes could be activated only in correct places. After all you could end up with teeth in your brain if it was left to chance without a plan in mind. Evolution’s chance processes fail most of all at this point. Think about it! (Ref. gene expression, mineralisation, ichthyology)
Evidence News vol. 15, No. 20
4 November 2015
Creation Research Australia