Corals of the Whitewater, Saluda and Liberty Formations in southeastern Indiana (section authored by Russ Kohrs)

During the Late Ordovician Period, much of the Midwestern United States was covered by a shallow sea. The entire region lay south of the Equator. This epicontinental sea received a great deal of sediment from the newly formed mountains that resulted from the early part of the Taconic Orogeny (Davis, 1998; Caster et al.,1955/1961). The tropical conditions in the area created an environment thriving with life. Some of this life came in the form of corals. Corals occupy a very important role in the oceans. Most corals build large reefs that provide habitats for many other forms of life. They are also very useful paleontologically as indicators of climate and latitude. Corals only live in shallow marine environments because they require clear, constantly moving water, oxic conditions, and sunlight. They are restricted to tropical climates because the warm water facilitates the precipitation of their calcium carbonate skeletons. These corals are called hermatypic corals, meaning that they incorporate a symbiotic algae called zooxanthellae into their tissues. These algae live off of the carbon dioxide in the water around the corals and release oxygen as a by-product, giving the coral polyps one of the key ingredients they need for survival. Ahermatypic corals live without symbiotic zooxanthellae, allowing them to occupy a greater variety of depths. They can also live at shallow depths, but can also be found at depths of 6,000 feet and temperatures 1 degree C above freezing.

Russ Kohrs, Junior Geology and Archaeology major at The College of Wooster. Russ is from Sagamore Hills, Ohio.

Protaraea richmondensis, an encrusting heliolitid coral.

The Whitewater Formation yielded the best and really the only coral samples that were found. From the specimens that were collected, two species can be identified. These species are Protaraea richmondensis, a heliolitid coral, and Grewingkia canadensis, a rugosan coral. Both of these species are common in the deepest parts of the shallow shelf environment of Late Ordovician seas. Rugosan corals, like G. canadensis, have also been given the nickname "horn corals" because of their characteristic shape. These Cincinnatian corals are solitary. They were the most abundant corals of the Paleozoic. A single "horn coral" is actually an entire corallite. The most distinguishing internal features of this group of corals are the vertical septa that radiate out from a central pillar called a columella. The polyp of this coral lived in the calice, or cup, located on the top of the corallum. This polyp would grow upward, making the corallite behind it progressively larger. The material used to create the corallite was calcium carbonate, most likely calcite and not aragonite (Babcock, 1996). These corals are found exclusively in Ordovician to Pennsylvanian rocks in Ohio.

The heliolitid corals, such as P. richmondensis, were exclusively colonial. Their skeletons were also made of calcite. These corals have twelve laminar septa. Each star shaped depression is a small corallite. These corallites are separated by a coenosteum which is secreted by parts of the polyp that lie outside of each corallite. They can be mistaken as tabulate corals, but are distinguished through a lack of connecting tubes and a lack of pores between corallites. These corals are encrusters and may branch their coralla in a number of different ways, lenticularly, hemispherically, totally erect, or in laminar to massive forms. These corals can be found from the Late Ordovician to the Devonian. Babcock, L. E. 1996. Phylum Cnidaria, p. 70-89. In Feldman, R. M. and M. Hackathorn, Bulletin 70, Fossils of Ohio, Ohio Division of Geologic Survey, Columbus. Caster, K. E., E. A. Dalve, and J. K. Pope, 1955, 1961. Elementary Guide to the Fossils and Strata of the Ordovician in the Viscinity of Cincinnati, Ohio. Cincinnati Museum of Natural History, Cincinnati. Davis, R. A. 1998. Cincinnati Fossils: An Elementary Guide to the Odovician Rocks and Fossils of the Cincinnati, Ohio, Region, Cincinnati Museum Center, Cincinnati.

Grewingkia canadensis, a typical Cincinnatian rugosan coral.

Polished transverse section of Grewingkia canadensis, clearly showing the radiating septa.