There are many kinds of fossil fish along the Jurassic Coast – but not all of them are like the fish we know today. Most were covered in armoured scales that didn’t rot, creating a perfect fish-shaped fossil. Other species, like sharks and rays, rotted completely leaving only their teeth behind.
Most of the fossil fish on the Jurassic Coast are very different from our ‘modern’ fish. They were heavily armoured with scales made of hard enamel that preserved well –which is why the fossil fish look so amazing. A classic example is Dapedium, on display at Lyme Regis Museum and Dorset County Museum. The specimen on the right is a fish from the purbeck Beds on Portland.
But Pholidophorus, found in the Lower Jurassic rocks around Lyme Regis doesn’t have the thick armoured scales. It is one of the earliest ancestors to modern fish like cod and mackerel.
A load of rot!
The skeletons of sharks and rays are made of cartilage (which isn’t as hard and rigid as bone), so usually only their teeth and fin spines are preserved as fossils.
Fossils show that sharks and rays have hardly altered in millions of years. In fact, a shark is so well adapted to its environment and way of life that it hasn’t needed to change at all.
Sharks teeth (right) are hard and were shed regularly through life which is why they can be very common in some layers of the rock sequence.
Most sharks have sharp, pointed teeth used for gripping and tearing their prey. Sharks continually shed their teeth, meaning they can have many thousands over their lifetime. So shark’s teeth can be very common as fossils.
Rays and most other fish have round or flattened teeth that form an upper and lower palate, which they use to crush prey like shellfish. But not all fish are the same. Have you ever looked inside a cod’s mouth?