Ordovician Period
470 million years ago

Ordovician marine scene

This is what you might have seen on a shallow sea floor 470 million years ago. The big tentacled fellow in the middle and his friends in the background were the dominant predators of that time. These cephalopods were distant relatives of squids and octopi with large, straight shells that could reach nine feet in length! The big one has snared a trilobite with its tentacles. Trilobites were one of the first arthropods to exist on Earth.

In the foreground are some corals, belonging to an extinct group known as rugose corals which are distantly related to the corals of today.

Below are fossils of the trilobite Ceraurus, the rugose coral Zaphrentis, and the straight-shelled nautiloid Orthoceras.

Fossil trilobite, coral, and nautiloid

Ordovician marine scene by Karen Carr, © Indiana State Museum and Historic Sites; Trilobite and nautiloid © UCMP; Coral by Sarah Rieboldt, © UCMP.

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