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