The enamel on your teeth came from prehistoric fish
A new study combining genes and 420 million year old fossils reveals that our tooth enamel developed from fish scales.
A team of palaeontologists and geneticists have discovered the surprising evolutionary origin of tooth enamel in something as unlikely as prehistoric fish scales.
"It's a great surprise, because today enamel performs an important function for our teeth. That's why we have it, "says co-author Professor Per Erik Ahlberg, from the Department of Organismal Biology, Uppsala University, Sweden.
The new study has been published in Nature.
Scientist: exciting new research
Palaeontologist Dr Jesper Mílan, curator at the Geoscience Museum in Faxe, Denmark, is enthusiastic about the new research.
"It's a really exciting study, which shows how nature's mechanisms operate so marvellously," says Mílan, who was not involved in the study.
"Who would’ve thought that something as different as fish scales and the enamel on our teeth actually have a common evolutionary origin?" he says.
Enamel is the strongest tissue in vertebrates. It provides our teeth with a protective coating.
Ancient fish covered in enamel
In the new study, lead-author Qingming Qu from the Department of Organismal Biology, Uppsala University, studied fossils of Psarolepsis--a fish from the Devonian period about 420 million years ago that predate the first land animals.
He studied ultrathin slices of the fossil fish under a microscope and discovered tiny structures that resembled enamel.
This protective enamel formed a type of armour and covered the entire body, including small dermal dentils, which are little tooth-like scales on the outer surface of the fish’s body.
The only place that did not have any tell-tale signs of enamel was, surprisingly, the teeth.
Similar characteristics are found in a species of fish called the gar, or Lepisosteus, a type of ray-finned bony fish.
DNA: the missing piece of the puzzle
Co-author Tatjana Haitina is an evolutionary biologist from the Department of Organismal Biology, Uppsala University. She studies ancient genetic material, and is interested in how animal genes evolved over time.
Haitana investigated the genome of living Lepisosteus, which was sequenced by Broad Institute in the US. She discovered that this archaic species of fish carried two out of our three genes associated with enamel: enamelin and ameloblastin.
What’s more, these genes are only expressed in Lepisosteus’ skin, which indicates that their scales are actually coated with a similar type of enamel that coats our teeth.
Enamel developed from armour to sharp weapon
But does our modern day teeth enamel really share an evolutionary origin with ancient fish body armour?
The answer lies in another fossilised fish: Andreolepis.
Andreolepis are even older than the 420 million year old Psarolepsis fish, whose head and body were covered in enamel. But Andreolepis have no enamel on their head, only on the rest of the body. Neither fish had tooth enamel.
Along with other fossils accounts, Ahlberg and his team built up a history of enamel evolution in the fish.
Working forwards from Andreolepis, enamel started on the body as a kind of protective armour. Later, it expanded to cover the head as seen on Psarolepsis. Later still, our fishy ancestors finally developed an enamel coating on their teeth.
"Enamel is a huge advantage because the teeth become sharper and tougher so they can withstand more wear," says Ahlberg.
Why did fish loose their body armour?
According to Ahlberg, a “body armour” simply became redundant when fish developed into faster swimmers with better manoeuvrability.
This springs from previous studies that have shown the enamel coating on Lepisosteus has another function besides offering the fish a protective outer coating. It is also helps to fasten many of the body’s large muscles.
"Ray-finned fish [like Lepisosteus] seem to have strengthened their ribs and backbone [as they evolved] whilst their scales have become lighter and smaller," he says.
In other words, the frame upon which the muscles are attached have moved from the outside of the body to the inside. This has probably made the fish a bit faster and more manoeuvrable, making the need for external body armour redundant.
Read the Danish version of this article on Videnskab.dk
Translated by: Catherine Jex