With mouths closed, the older, smaller teeth of the ancestors of today’s sharks stood upright on the jaw, while the younger and larger teeth pointed towards the tongue and were thus invisible when the mouth was closed. (Illustration: Christian Klug, UZH)
With mouths closed, the older, smaller teeth of the ancestors of today's sharks stood upright on the jaw, while the younger and larger teeth pointed towards the tongue and were thus invisible when the mouth was closed. (Illustration: Christian Klug, UZH) - Some, if not all, early sharks that lived 300 to 400 million years ago not only dropped their lower jaws downward but rotated them outwards when opening their mouths. This enabled them to make the best of their largest, sharpest and inward-facing teeth when catching prey, paleontologists at the Universities of Zurich and Chicago have now shown using CT scanning and 3D printing. Many modern sharks have row upon row of formidable sharp teeth that constantly regrow and can easily be seen if their mouths are just slightly opened. But this was not always the case. The teeth in the ancestors of today's cartilaginous fish (chondrichthyan), which include sharks, rays and chimaeras, were replaced more slowly. With mouths closed, the older, smaller and worn out teeth of sharks stood upright on the jaw, while the younger and larger teeth pointed towards the tongue and were thus invisible when the mouth was closed.
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