Fossil Corals
Ancient reef-builders — corals have constructed Earth's reefs for over 500 million years, from Cambrian archaeocyaths to the massive rugose and tabulate colonies of the Palaeozoic.
Overview
Corals are colonial (occasionally solitary) cnidarians that secrete calcium-carbonate skeletons and build reefs. The fossil record is dominated by the extinct rugose ('horn') corals and tabulate corals of the Palaeozoic, succeeded by the scleractinian corals that build modern reefs.
Quick Facts
Key Characteristics
- •Rugose corals: solitary horn shapes or colonies, with septa arranged in fours
- •Tabulate corals: colonies of polygonal tubes divided by horizontal tabulae
- •Scleractinian corals: aragonitic skeletons with six-fold septal symmetry, usually symbiotic with algae
- •Colonies grow in massive, branching or sheet forms recording water energy and depth
Fossil Record
Corals are major reef-frame builders through the Phanerozoic: Silurian and Devonian reefs of North America and Europe, Mississippian coral beds of Iowa and Missouri, and vast Cenozoic reef limestones worldwide preserve them in abundance.
Global Distribution
Global in warm-water marine rocks, with classic Palaeozoic faunas in North America, Europe and Asia.
Evolutionary & Scientific Importance
Coral reefs are Earth's largest biological structures, making corals key to reef evolution, palaeoclimate (their skeletons record temperature and chemistry), and the repeated collapse of reef ecosystems at mass extinctions.
Classification
The origin of scleractinian corals is debated — 'naked' coral hypotheses suggest skeleton loss and re-mineralisation in their history.