Rugose corals are often called horn corals because many species have a horn shape. All horn corals live in a cup called a calyx (KAY-licks). The calyx often has radially alligned ridges or grooves, which are called septa. These septa were the skeletal support plates for the coral animal or polyp. When alive, the horn-shaped skeleton of the coral animal was attached to the sea floor with the pointy end down. The living coral polyp lived on the top of the skeleton with its arms or tentacles pointing upward.

In Devonian strata, some horn corals grew to large lengths. The horn coral Siphonophrentis giganteas may have reached lengths of 6 feet!

Siphonophrentis
Siphonophrentis

Siphonophrentis is a common type of horn coral in the Jeffersonville Limestone at the Falls of the Ohio near Louisville. This specimen is 18 cm long, but specimens as long as 1.8 m (6 ft) have been reported. Most Siphonophrentis corals are relatively thick, compared to other rugose corals. This specimen was donated to the Kentucky Geological Survey by R. Todd Hendricks and shown in Greb, 1989, p. 14, Fig. 17-3.

Siphonophrentis

Siphonophrentis as it appears in the Jeffersonville Limestone at the Falls of the Ohio near Louisville. Some of the calices of these corals are very wide and indicate that they were occupied by large coral animals (polyps). There is some debate as to whether these corals stood upright off of the sea bottom or were curled up on their side, laterally across the sea floor. Many are straight suggesting they stood upright. Other genera are curled or irregular in shape and definitely layed on their side as they grew.

Siphonophrentis

Siphonophrentis as it appears in the Jeffersonville Limestone at the Falls of the Ohio near Louisville. Some of the calices of these corals are very wide and indicate that they were occupied by large coral animals (polyps). There is some debate as to whether these corals stood upright off of the sea bottom or were curled up on their side, laterally across the sea floor. Many are straight suggesting they stood upright. Other genera are curled or irregular in shape and definitely layed on their side as they grew.

Scenophyllum

Scenophyllum is another type of rugose coral common in the Jeffersonville Limestone (Devonian). It can be distinguished from other rugose corals by the nipple-like protrusion within it's calyx (see detail). Scenophyllum is generally narrower than Siphonophrentis. This specimen's calyx is 2 cm across. The coral is 16 cm long. It was collected by R. Todd Hendricks and donated to the Kentucky Geological Survey.
It is pictured in Greb and others, 1993, Fossil beds of the Falls of the Ohio, Fig. 13f, p. 13.

 

Tabulophyllum

Some rugose horn corals have shapes that appear as cups (calices) within cups. Sometimes as if the cups were stacked one inside the other. This is Tabulophyllum from the Jeffersonville Limestone at the Falls of the Ohio. The lens cap is for scale. Tabulophyllum often has a twisting shape. Like most horn corals, this stacked-cup form started out as a single calyx (1 in the diagram on the right), growing upward from the sea bottom (2 in the diagram), until it was knocked over by storms or strong currents (3 in diagram). These types of coral would then sprout a new calyx (4 in diagram), which grew upwards, until it was knocked down. This might happen several times during the corals life, resulting in twisted, cup-in-cup shapes. (Diagram is modified from Greb and others, 1993, Fig. 14, p. 14. Identification is by Alan Goldstein.)

Horn corals came in many different sizes. Small horn corals can be found in rocks of Ordovician, Silurian, Devonian, Mississippian, and less commonly in Pennsylvanian strata in Kentucky.

Enallophrentis corals are common in Devonian-age limestones. They range in size from 3 to 7 cm. Enallophrentis inflata (Hall) is outwardly similar to another small horn coral called Zaphrentis, which also occurs in Devonian-age limestones. You can tell the two corals apart by looking at the grooves (called septa) within the coral calyx (the cup). The septa are where the coral animals (polyps) attached when the corals were alive. Enallophrentis has smooth septa, while Zaphrentis has jagged septa (from Greb et al., 1993, Fig. 13a-b).

 

Another example of a rugose coral. The orange color of the specimen is caused by mineralization. The limestone in which the fossil originally formed has been replaced by silica (quartz). Found in the Louisville area and donated to the Kentucky Geological Survey by R. Todd Hendricks.

 

Another example of Enallophrentis inflata, a type of rugose coral. Found in the Louisville area and donated to the Kentucky Geological Survey by R. Todd Hendricks. All Enallophrentis identifications by Alan Goldstein

 

 

Rugose corals can be found in the basal parts of some dark gray shales of Pennsylvanian strata in both of Kentucky's coal fields. This Lophophyllidium specimen is 3 cm long and was collected in the Kendrick Shale Member in eastern Kentucky.

 

 

Last Modified on 2019-04-11
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