Armour-plated fish and the evolution of dentists

The discovery of small spikes lining the mouths of primitive fossil fish reveal surprising new details about how early animals fed. New research published today in a Royal Society paper sheds light on how teeth evolved.

Primitive fish did not have jaws or fins but were covered in rigid bony scales and resembled small armour-plated submarines. Dr Mark Purnell, a palaeontologist at the University of Leicester, has discovered that heterostracans, one of the most important groups of these early fish, had small spiky structures lining the inside edge of the mouth. These structures were made of hard dentine and were possibly the precursors of teeth as we know them today.

Only animals with backbones have true teeth, and the enamel and dentine of which they are made are the hardest materials in the body. ‘If you go looking for fossils of sharks, dinosaurs or any other vertebrate animal, you are more likely to find teeth than bones. Yet, surprisingly, mystery and uncertainty still surround the questions of when teeth first evolved and what they were used for,’ says Dr Purnell.

These new discoveries indicate that these early ‘teeth’ were not separated, individual structures but were modified from the armour plating that shielded the outside of the body. They had sharp points, cusps and ridges, but, unlike teeth, these points all faced forwards, and the fish could not have bitten or grabbed their food, or consumed anything but very small or soft items. This new evidence suggests that these early ‘teeth’ evolved not in a ferocious biting creature, but from the bony scales of a slime-slurping sucker.

Understanding how, when, and why animals first cut their teeth more than 400 million years ago is fundamental to understanding why the world around us is as it is. ‘Imagine a world without teeth – the history of life would certainly have taken a different course. Sharks would no longer be terrifying and dentists, more frightening to many people, would never have evolved,’ adds Dr Purnell.