Fish fossils provide new insight into the origins of teeth

The analysis of ancient fish fossils has revealed the developmental origins of teeth. Using high-resolution X-ray imaging, scientists have identified an evolutionary relationship between teeth and hard structures called dermal odontodes.

Study lead author Donglei Chen is a researcher in the Department of Organismal Biology at Uppsala University.

Odontodes are made of dentine, the main substance in ivory. Teeth are an example of odontodes, but some animals also have them on their skin in the form of the tooth-like “scales” known as dermal odontodes.

“Teeth and dermal odontodes are thought to have evolved separately because they seem to develop in different ways,” said Chen. “However, most of what we know is limited to modern sharks in which the difference between these structures has become very distinct. To understand the relationship between the two more clearly, we needed to turn to the fossil record.”

The research was focused on fossils of one of the earliest bony fishes called Lophosteus, which lived more than 400 million years ago. The fish represents an early stage of tooth evolution, not long after teeth and dermal odontodes may have diverged. 

The researchers used high-resolution X-ray imaging to look at the three-dimensional structure of odontodes in Lophosteus at different stages of development. The study revealed that the appearance of odontodes were similar during early development, but they changed depending on whether they grew in the mouth or on the face of the fish. This finding indicates the presence of different chemical signals in each area directing odontode development. 

In the later stages, some dermal odontodes would move from the face to the mouth and begin to look like teeth, suggesting that both types are made by the same developmental system rather than by separate systems.

“In addition to casting light on the early evolution of our own teeth, our results point to a previously unrecognised evolutionary-developmental relationship between teeth and dermal odontodes,” said study senior author Dr. Per Ahlberg.

“This has potential implications for understanding the signaling that occurs during development and could inspire new lines of developmental research in other organisms.”

The study is published in the journal eLife.

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By Chrissy Sexton, Earth.com Staff Writer