The Difference Between...Rugose, Tabulate and Scleractinian corals

This is going to be a series of posts that look at fossils that are either difficult to

Rugose coral. Image credit: paleo.cortland.edu

differentiate or can be easily confused.

This post will look at three types of corals; rugose, tabulate and scleractinian.

First of all, there is the geological context of these corals, in partcular what age the sediments will be that you find them in. Rugose corals are found in Ordovician to Permian sediments, being wiped out at the Permian extinction. Tabulate corals also have the same range, so this would not be useful if you were trying to differentiate the two using geology. However, scleractinian corals have a younger range, from the Triassic to recent times. giving a feature to differentiate this coral from the other two.

Tabulate coral. Image credit: fossillady.wordpress.com

Scleractinian coral. Image credit: hoopermuseum.earthsci.carleton.ca

When trying to identify if your coral is tabulate or not, look at whether or not your fossil is colonial or solitary. Tabulate fossils are almost exclusively colonial. It's difficult to differentiate Scleractinian and Rugose fossils this way as both have colonial and solitary species.

Scleractinian and Rugose corals both also have well developed septa, so this cannot be used to tell the difference. But again, tabulate corals have weak or absent septa. The tabulae can be used to identify Scleractinians easily as they are usually absent in these corals. They are well developed in tabulate and most rugose possess tabulae.

Symmetry is useful for differentiating Rugose corals from tabulate and scleractinians. The symmetry in rugose is bilateral, meaning that two identical halves can be created, humans are bilaterally symmetrical. However, tabulates and scleractinians have radial symmetry.

Scleractinian skeletons are made from aragonite which is unstable in fossilisation, whereas the tabulate and rugose corals have calcite skeletons.

Summary:
Rugose: Ordovician to Permian. Well developed septa. Bilaterally symmetrical. Colonial and solitary. Most possess tabulae. Calcite skeleton.

Tabulate: Ordovician to Permian. Weak or absent septa. Radial symmetry. Always colonial. Well developed tabulae. Calcite skeleton.

Scleractinian: Triassic to Recent. Well developed septa. Radial symmetry. Colonial and solitary. Absent tabulae. Aragonite skeleton.

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