The outside-in and inside-out hypotheses about where teeth came from are both valid.
The Ischyrhiza mira species was an extinct sawfish that lived in North America around 100 million years ago.
The sawsharks and sawfishes had jagged spikes around their snouts to ward off predatory animals. rostral denticles are believed to be modified versions of the scales on the rest of the body
The team looked at the outer layer of the snout spikes to see if there was a relationship between rostral denticles and scales.
Todd Cook from Pennsylvania State University says that I. mira's rostral denticle enameloid was not easy to understand. It was much more complicated than the scales on the body.
The organization of the teeth in this ancient sawfish was similar to that of modern shark teeth.
The way in which the shark teeth are made is similar to the way the fossil is made.
Microcrystals are positioned on the surface of the tooth. The shark teeth have different orientations that give them strength and resistance.
Cook says that the bundled microcrystal arrangement of the I. mira's rostral denticles served as a way to endure mechanical forces.
If one came after the other, the outside-in hypothesis about where teeth came from, would be more logical.
The researchers did not intend to look into the evolutionary history of teeth when they began their analysis, but their findings could have a significant impact on future studies.
It is more likely that the teeth inside our mouths are fish scales than it is that they are marine creatures.
The outside-in hypothesis is supported by the fact that scales have the ability to evolve a complex tooth-like enameloid outside of the mouth.
The research was published in a journal
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