Ancient fish holds key to teeth origin

17 October 2012

The oldest teeth have been identified in an ancient fish, revealing clues to the origin of our own, scientists report in Nature today.

Scientists found evidence of teeth in the ancient fish species Compagopiscis croucheri, which belongs to the extinct group of fishes called Placodermi.

Placoderms lived in the Devonian Period (416-359 million years ago) and they are the most primitive jawed vertebrates (back-boned animals) known.

By showing that this animal had teeth rather than tooth-like jawbone structures, researchers have found the earliest occurrence of teeth, and so revealed their evolutionary origin.

The international team was led by fossil expert (palaeontologist) Martin Ruecklin of the University of Bristol and included the Natural History Museum's fossil expert Zerina Johanson.

With the help of physicists at the Swiss Light Source synchrotron they analysed fossils of Compagopiscis croucheri using powerful X-rays

This non-destructive method allowed the team to investigate in great detail the developmental stages of how the jaws grew and how teeth were successively added to the jaw

Virtual section through the jaw of placoderm Compagopiscis crouchier

Virtual reconstruction of section through the lower jaw of fish Compagopiscis crouchier showing a tooth-row and growth lines that scientists used to reconstruct the developmental stages. © Martin Ruecklin, University of Bristol

The fossil data was analysed with data from comparisons with living vertebrates, and the team was able to make virtual reconstructions showing the tooth developmental stages in Compagopiscis.

Diagram showing virtual the development of the teeth and jaws

Diagram showing virtual reconstructions of development of the teeth and jaws. © Martin Ruecklin, University of Bristol

'We were able to visualise every tissue, cell and growth line within the bony jaws, allowing us to study the development of the jaws and teeth,' said Ruecklin

'We could then make comparisons with the embryology of living vertebrates, thus demonstrating that placoderms possessed teeth.'

The team studied Compagopiscis fossils, including those from the Museum collections, where there are many well-preserved and complete specimens.

Johanson adds, 'These wonderfully preserved fossils from Australia yield many secrets of our evolutionary ancestry but research has been held back waiting for the kind of non-destructive technology that we used in this study.'

'Without the collaborations between palaeontologists and physicists, our evolutionary history would remain hidden in the rocks'.

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