Temporal range: 488–251.4Ma Ordovician–Permian
|Solitary rugose coral (Grewingkia) in three views; Ordovician, Indiana. Scale bar is 2.0 cm.|
Solitary rugosans (e.g., Caninia, Lophophyllidium, Neozaphrentis, Streptelasma) are often referred to as horn corals because of a unique horn-shaped chamber with a wrinkled, or rugose, wall. Some solitary rugosans reached nearly a meter in length. However, some species of rugose corals could form large colonies (e.g., Lithostrotion). When radiating septa were present, they were usually in multiples of four, hence Tetracoralla in contrast to modern Hexacoralla, colonial polyps generally with sixfold symmetry.
Rugose corals have a skeleton made of calcite that is often fossilized. Like modern corals (Scleractinia), rugose corals were invariably benthic, living on the sea floor or in a reef-framework. Although there is no direct proof, it is inferred that these Palaeozoic corals possessed stinging cells to capture prey. They also had tentacles to help them catch prey. Technically they were carnivores, but prey-size was so small they are often referred to as microcarnivores.
Rugose coral always show tabulae, these are horizontal plates that divide the corallite skeleton, the corallites are usually large relative to different types of coral. Rugose will sometimes have dissepiments present, these are curved plates connected to septa and tabulae. The symmetry can be distinguished by the orientation of septa in a transverse section of the coral. Rugose always display bilateral symmetry whereas tabulate and scleractinian show radial symmetry. Initially there are only 6 major septa, later minor septa are added in the 4 resulting spaces. the complex arrangement of septa is diagnostic of Rugose coral. Rugose will also always have a columella, this is an axial rod which supports the septa running up the centre of the corallite, it is seen in Rugose coral because they are mainly solitary and so requires the extra support whereas, Tabulate coral for example has no columella as they are always colonial and rely on the support of neighbouring corallites.
|Horn coral fossil|
- Color reconstruction of the Devonian coral Heliophyllum halli at www.emilydamstra.com
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