Tiny fish illuminates tooth fairy mystery

by Mary Caperton Morton
Thursday, February 16, 2017

When kids lose their milk teeth, the roots shrivel up and just the outer enamel falls out — a process known as basal resorption. Now, the discovery of a tiny jawbone from a 424-million-year-old fossil fish is shedding light on the origin of our modern mode of tooth replacement.

Using a microscopic imaging technique called synchrotron x-ray tomography, a team led by Donglei Chen of Uppsala University in Sweden created a three-dimensional map of the entire sequence of tooth loss and replacement in the fossil specimen without damaging it. The study marks the first time that fossil dentition has been analyzed in such detail without cutting a specimen into sections.

“We can follow the process of growth and resorption right down to [the] cellular level, almost like in a living animal,” said Per Ahlberg, Chen’s colleague at Uppsala and a co-author of a new study in Nature reporting the findings, in a statement.

The researchers describe how the ancient fish replaced its teeth through basal resorption, and cite this as the earliest known example of the technique. “Every time a tooth was shed, the resorption process created a hollow where it had been attached,” Chen said. The same process is seen in living bony fish, such as gar and bichir, with new replacement teeth developing alongside old teeth rather than underneath them, as in human toddlers.

“As we apply this technique to more early vertebrates, we will come to understand their life processes much better — and no doubt we will be in for some major surprises,” Ahlberg said.

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