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4 Aug 2020 3:21
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  •   Home > News > International

    Earliest ever fossil teeth shed light on the evolution of modern pearly whites

    A study of primitive fish fossils reveals the system by which humans, and other jawed vertebrates including sharks, grow new teeth is over 400 million years old.

    From sharks to humans, jawed vertebrates have very neat and symmetrical sets of teeth.

    But at what point in the amazing history of life on Earth did the system for growing teeth in such an orderly fashion evolve?

    Previous research has suggested it happened in a step-by-step way over the aeons, but now researchers claim this dental plan was there from day one.

    Palaeontologist Per Ahlberg from the University of Uppsala in Sweden and colleagues have reported their study of fossil teeth from fish that lived over 400 million years ago in the latest issue of the journal Science.

    "If you look at teeth — from Jaws to us — you will notice there is a geometrical neatness," Professor Ahlberg said.

    "They are carefully positioned, and new teeth are added in a very organised way."

    This is just as well, because imagine how hard it would be for teeth to do their job if, say, you lost a front milk tooth and a canine tooth grew in its place?

    "The tight organisation of what grows where, and in what time succession, is crucial to having a dentition that works," Professor Ahlberg said.

    All modern vertebrates have the same basic system where new teeth emerge from the inside of the jawline and move to the outside.

    You can see this clearly in a shark, but surprisingly enough this also applies in humans.

    It's just that because we have a flattened face, rather than a snout, it looks like our new teeth come from under or above the old teeth.

    Of course sharks differ from humans because they have a continuous supply of new teeth and humans only grow one set of new teeth — although some researchers hope to change this.

    Previous research on a now extinct ancient group of armoured fish called placoderms — the first fish with jaws — suggest their dentition was quite different from modern vertebrates.

    "They originate from a central point whereas with modern jawed vertebrates the new teeth form in place behind each older tooth," Professor Ahlberg said.

    But now he and colleagues have used powerful synchrotron x-rays to look at the teeth in the fossil skulls of even more primitive fish than those studied before.

    "We're right down where jaws first originated," Professor Ahlberg said.

    The reef-dwelling fish the researchers studied, including one called Radotina, swam in the oceans over 409 million years ago, and likely evolved around 430 million years ago, he said.

    The fish were quite small — and likely hid from predators in empty shells.

    Professor Ahlberg and team were able to image the inside of the skull in high resolution and see where new teeth were emerging from.

    And they found the same basic system as in modern jawed vertebrates like sharks and humans.

    "We have a shared ancestral pattern."

    The fossils studied by the researchers were originally found in quarries on the outskirts of Prague where limestone was being split for paving stones 100 years ago.

    "They've been sitting in Prague museum revered as very important but not studied," Professor Ahlberg said.

    "The synchrotron allowed us for the first time to look inside these fossils and dissect out their anatomy ... and there were the teeth!"

    Australian researchers have welcomed the study.

    "This is an amazing discovery and it's a big step in unravelling the origins of teeth," said Kate Trinajstic from Curtin University, who was involved in earlier studies of placoderm teeth.

    "It's the first time we've seen a common developmental mechanism across placoderms, sharks, bony fish and land animals."

    David Bellwood of James Cook University, who studies the evolution and ecology of fish, said the research offered valuable new insights into the early evolution of teeth in jawed fish.

    "Teeth are literally on the cutting edge of ecological interactions and shape how fishes obtain their food," he said.

    Professor Bellwood said these earliest teeth appeared capable of "crushing, cutting, and grasping", suggesting their owners had a diverse diet.

    © 2020 ABC Australian Broadcasting Corporation. All rights reserved

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