Fish that lived long before the dinosaurs featured the world's first known teeth, according to a new paper that suggests all teeth -- including those of humans -- originally evolved from fish scales.
The earliest teeth date to at least 410 million years ago, according to the paper, published in the journal Biology Letters. It describes in detail a tiny tooth plate from the fossil fish Romundina stellina that fortuitously was found in box, which had been in storage for more than 40 years.
"In the tree of life, they (the teeth) are the earliest ones, but they are not the oldest ones," lead author Martin Rücklin of the Naturalis Biodiversity Center in The Netherlands told Discovery News.
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He explained that Romundina is a placoderm, meaning an extinct class of armored fish. Older remains of this fish and related species have been found, but "jaws with teeth are not yet found" associated with these fossil bits and pieces, Rücklin said.
The specimen that he and colleague Philip Donoghue of the University of Bristol studied, however, reveals early teeth in striking detail.
The researchers used powerful computing to combine thousands of X-rays of the fish's tooth plate. They then produced computer models reconstructing the growth of the first known teeth, which were as fishy as one might expect.
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"Our data show that teeth and scales of Romundina are made of the same tissues, and these are also found in our teeth," Rücklin explained. "This is in agreement with the idea that scales evolved first and teeth derived from them."
As for what prompted this evolution, the precise answer remains a mystery for now, but there are some intriguing clues.
Based on other Romundina fossils, researchers suspect this fish was an active predator close to the water's surface.
"Jaws and teeth are needed to process larger food items, and Romundina represents a predator that was able to swim actively in the water column hunting," Rücklin said.
The fish had paired nasal openings and laterally facing eyes, suggesting that it was built perfectly for hunting animals similar to today's octopus and squid, as well as crustaceans and other fish.
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Yet another theory holds that there was an evolutionary arms race that pitted jawless ocean predators against those with jaws and teeth. The researchers, however, found that the earliest teeth developed somewhat independently from jaws, since both the teeth and jaws derived from separate components. While teeth evolved from scales, it is believed that jaws evolved from fish bones.
In terms of the earliest tooth configurations, the teeth of Romundina were small yet numerous. They were made out of materials very similar to those found in today's teeth: enameloid and dentine. Like enamel in human teeth, the enameloid in the prehistoric fish was a very hard tissue that formed a cap, functioning to protect each tooth.
John Long, a professor at Flinders University, remarked, "This is a really significant discovery that proves the origins of true teeth are deeper down the vertebrate tree, or another mystery of evolution still to be solved."
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Philippe Janvier of Paris' National Museum of Natural History said that new findings, "throw light on the structure of the most primitive teeth known to date."
Rücklin and his team recently received a grant from the Netherlands Organization for Scientific Research to further investigate the evolution of jaws and teeth.
Such research over the next five years should not only answer existing questions about tooth evolution, but also how environmental changes can lead to profound changes in animals -- such as prompting jawless creatures to evolve jaws that, to this day, remain critical to the survival of so many species, including our own.