Many different kinds of reefs have existed during the past 500 million years.

The patches of green show times when there were lots of reefs.

The red lines above them show when those reefs went extinct.

Just like today many other animals, such as mollusks, crustaceans, and sponges depended upon the habitat created by these reefs.

What happened to the animals living in the reefs (Reef Dwellers) when the animals that built the reefs (Reef Builders) went extinct?

CLICK on the highlighted periods to learn more about these reefs.