CAMBRIAN to PLEISTOCENE PERIOD: 542 million years ago - 10,000 years ago
Fossil corals were simple marine invertebrates that possessed a sac-like body called a polyp with a mouth and tentacles. As carnivores, they would immobilize or kill their prey with their stinging tentacles then swallow their prey and later expel the wastes through the same mouth. They formed a dense outer skeleton of calcium carbonate which, when living in large colonies of thousands of cloned individuals, formed a massive structure. The complex folds in their stomach cavity can be seen in the wondrous detail left behind in their skeletons. Modern corals today share a symbiotic relationship with algae that covers their body tissue. The algae supplement the coral with oxygen which most likely was the case in prehistoric times, as well.
Prehistoric corals are believed to have thrived in the same environments that modern corals prefer - clean, warm oceans of normal salinity levels. Solitary corals were present in oceans of soft, muddy bottoms while horn corals and colonial corals preferred hard sea floors to attach themselves.