Fossil Facts > Death of an Ichthyosaur

The death of an ichthyosaur & what its remains tell us (pics with notes): An ichthyosaur swims in a shallow Jurassic sea. It’s a marine reptile. Several species swam here in early #Jurassic period. This one is Ichthyosaurus communis (most common species): a generalist feeder.

Also in the Jurassic seas were a range of fish. Here is a Dapedium, a well-known fish from #Lyme – a carnivore with powerful jaws & crushing teeth. Its thick scales & head plates act as armour.

Our Dapedium is caught. Its scales no defence against the ichthyosaurs teeth. It’s quickly swallowed. If the ichthyosaur dies soon after its meal, scales of the Dapedium might be preserved in its stomach. If not, they’ll be passed as poo (sometimes preserved as coprolites).

Eventually our ichthyosaur dies. If it dies of starvation/disease, its whole body sinks. Dead ichthyosaurs often lay on their side (bigger ones on bellies). Here, seafloor water was often still & lacking in oxygen. This left the carcass to decompose without being scattered.

As the flesh rots, several things happen. The teeth can fall out of the jaw. Ichthyosaur teeth aren’t in sockets but are held in a groove running along the jaw. The teeth on the side of the jaw in the mud are more likely to stay in the jaw.
The front fins start to decay.

As the animal is on its side, one paddle rests on the mud. Bones of this paddle stay undisturbed. Other fin doesn’t survive as well. As its flesh rots it disintegrates & the bones of the fin fall to the seafloor. They scatter on the floor & on top of other fin.