Scientists in Australia and the United Kingdom have discovered the sharpest teeth ever recorded in history – with tips measuring just two micrometres across – that belong to a long-extinct prehistoric fish. The study, presented in the journal Proceedings of the Royal Society B, was funded in part by the EVOLVING TEETH ('Uncovering developmental and functional constraints on the occupation of conodont tooth morphospace') project, which is backed by a Marie Curie Action grant worth EUR 198 260 under the EU's Seventh Framework Programme (FP7). The project involved teams from University of Bristol, UK, and Monash University, Australia, working together and using a very big machine to see some of the world's smallest fossils.
The results of this study provide insight on the potential eating habits of these conodonts, early vertebrates that kept their skeleton in their mouth and that lived some 500 million years ago. Fossils of conodonts, animals which resemble eels, are extremely rare. For a long time, what scientists knew about them was only what they derived from their tooth-like microfossils. This research suggests that conodonts evolved the first vertebrate dentitions.
'Conodonts had no other skeleton than the teeth in their mouths,' said Dr Alistair Evans from the School of Biological Sciences at Monash University in Australia, one of the study's authors. 'These came together a bit like scissors, to slice up food.'
Being so microscopic, the scientists realised that the teeth must work differently from the teeth of other animals, including humans. So with such small teeth, no jaws and weak muscles, researchers asked how could they possibly have worked as teeth?
The researchers found that the teeth indeed worked differently thanks to their sharpness.
'The conodonts took an alternative route through evolution to humans, who developed less efficient, but less breakable, blunter teeth, to which greater force can be applied by jaw muscles,' Dr Evans said. 'The sharpness of conodont teeth allowed them to overcome the limitations of their small size. Since pressure is simply force applied divided by area, to increase pressure you must either increase the force or shrink the area. Conodont evolution took the latter route, allowing them to apply enough pressure to break up their food,' he added.
'So next time you’re struggling through a tough Sunday roast, remember that conodonts evolved the tools for the job 500 million years ago,' said Dr David Jones from Bristol's School of Earth Sciences, another author of the study.
One of the major challengers the researchers faced was to determine how to analyse something which in size is one twentieth the width of a human hair.
Said Dr Jones: 'The first problem is: how do you analyse such tiny teeth? The answer: with a very big machine. We created high resolution three-dimensional models of the conodont elements using x-rays from a particle accelerator in Japan, using it like a giant computed tomography scanner. These virtual models were examined, leaving the original specimens untouched.'