The Coelacanth

The coelacanth is a living fossil, its appearance little changed in hundreds of millions of years. It evolved into roughly its current form approximately 400 million years ago. A new analysis of its scaly armour may reveal how it has stuck around for so long. The coelacanth fish has scales that can change their internal structure if they are pierced by a predator to stop cracks spreading.

Isopedin is a network of collagen bundles present in the scales of most fishes. The scales of coelacanths have a three-dimensional arrangement of this network which is similar to twisted plywood. The successive fibrous layers cross at an angle. These highly modified scales are known as cosmoid scales, and are only found on extinct fish species.