A study of a 100-million-year-old fish fossil has raised the theory of teeth origins that came from inside or outside the mouth. One theory holds that teeth form from external scales or come from the mouth, but neither theory has been sufficiently demonstrated.
Evolution of Teeth in Animals
They based their findings on the extinct prehistoric sawfish species, Ischyrhiza Mira, found in North America. It existed between 65 and 100 million years ago, and there is some supporting evidence for the outside theory, reported Science Alert.
Similar to the saw sharks and sawfishes that exist today, this creature possessed jagged spikes on the sides of its snout that helped keep predators while looking for food.
One theory holds that these rostral denticles, or external spikes, are supposed to be scales that change to serve different purposes on the rest of the body.
By closely examining the tough enameloid outer layer of the snout spikes, the researchers investigate the correlation between the rostral denticles and scales. With the help of these body parts, they noticed something unforeseen that astounded them in the theory of teeth origins.
The rostral denticle enameloid was far from simple, asserts vertebrate paleontologist Todd Cook of Pennsylvania State University. Instead, it was more complex than the same body scale enameloid, noted PSU EDU.
According to his description, the material in this ancient million-year-old fish fossil of a sawfish had a striking resemblance to that of a well-studied enameloid in a contemporary shark tooth.
One intriguing finding is that the material on the fossil has traits in common with those of shark teeth found today. It comprises bundles of fluorapatite microcrystals neatly arranged near the tooth's surface and more haphazardly arranged below.
Did Teeth Evolve From Fish Scales?
These layers are covered in densely packed microcrystals parallel to the tooth's surface. Shark teeth are durable and resistant to strain due to their different orientation, and it would seem that the ancient fish is no different.
Cook remarked that the dense arrangement of the microcrystals of I. Mira and the rostral denticles which developed resisted extreme stress.
Although it's not completely implausible, it is more logical if the scales and teeth developed independently of one another. Therefore, based on the evidence, teeth would develop from an outside-in hypothesis.
When the researchers started their analysis of rostral denticles on the fossil, they had no plan to look into the evolutionary past of teeth, but their research results may have a significant effect on future studies in this area.
As more resemblances between both the exteriors of sea organisms and the gnashers from within our mouths are realized, it would seem that the teeth within our mouths seem to be highly evolved fish scales. As parting thoughts, Cook asserted that the new finding gives direct proof to support the outside-in hypothesis, illustrating that scales can evolve a sophisticated tooth-like enameloid outside the mouth.
How teeth evolved from the parts of Ischyrhiza Mira shows that humans have some structures from other origins, like fish scales, for one, that was not expected. It seems a million-year-old fish fossil might settle the theory of teeth origins, which came from the rostral denticles of I. Mira, coming from the study, citing Science Daily
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