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The whole tooth and nothing but the tooth

By Mike, 2 November 2012 News

Skull of a placoderm, an ancient type of fish

Placoderms were an ancient fish – one of the first backboned animals to have jaws.
Image: Wikimedia commons/Tim Evanson BY-SA

Say cheese and flash that beautiful smile. You should be proud of those choppers; after all, teeth have been around for nearly half a billion years.

The fossilised teeth of backboned animals, or vertebrates, are a paleontologist’s dream – they’re tough enough to survive weathering and often contain distinctive features that reveal a lot about an animal’s diet. But when did the first tooth appear?

Winding back the clock roughly 440 million years, there’s an aquatic ancestor called the placoderm. These armoured fish provide us with the oldest evidence of vertebrate jaw bones. New body parts rarely pop into existence. Instead, a body part evolves or changes just enough to perform another job. In this case, the front gill slits of placoderm’s ancestors became useful for getting a grip on lunch.

There have been some big questions about when these early jaws sprouted teeth and if so, what those teeth might have been like. Were placoderms all gums? Did they have something like a toothy peg? Or could the first fish flash a sharp-looking grin?

Western Australia has well-preserved placoderm fossils with hints to help solve this mystery. However, the clues are inside the fossilised jaw bones. Cracking them open to take a peek is out of the question.

Instead, researchers from Curtin University, University of Bristol and London’s Natural History Museum worked with physicists in Switzerland using X-rays to peer inside the fossils. Only these X-rays are millions of times stronger than those at your local hospital, created by a type of particle accelerator called a synchrotron.

They found evidence of distinct structures that could be compared to what we’d today consider to be teeth. This suggests that teeth evolved not long after the first jaws appeared.

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