Corals: Reef Builders in Ancient and Modern Seas (PA-07)
Corals, brightly colored marine animals when alive, have lived in the sea as individuals and in colonies for about 475 million years. As each animal secretes an external skeleton, corals are prominent reef-building organisms. They are predatory even though they are attached and cannot move around. Tentacles armed with stinging cells are used to capture prey.

More than 400 million years ago many reefs existed in the seas that covered this region. Petroleum occurs in fossil reefs and in rocks structurally affected by reefs. Reef areas can be used for storing natural gas. And in Indiana, reefs are sources of excellent aggregate and high purity limestone. Thus geologists study ancient reefs just as they have studied corals for more than a century.

Our Hoosier State Beneath Us: Paleontology