Late Ordovician Paleontology, Sedimentology
and Stratigraphy in Ohio, Indiana and Kentucky
A Keck Geology Consortium Project
June 19 - July 16, 1999
The Upper Ordovician rocks of southwestern Ohio, southeastern Indiana, and northern Kentucky consist of alternating mudstones and fossiliferous limestones (Cuffey, 1998) which contain various bored organisms, including bryozoans, brachiopods, bivalves, and corals. These borings occur throughout the Cincinnatian rocks but are most prominent in the Whitewater Formation of Indiana and the Grant Lake Formation of Ohio and Kentucky. Although bored organisms are common in Cincinnatian rocks, generally they are overlooked and omitted from existing paleontologic literature. For example, only three borings, Petroxestes, Trypanites, and Ropalonaria, have been described from the Paleozoic of Ohio (Hannibal, 1996), although a diversity of borings that do not fit these descriptions exist throughout the Cincinnatian. Similarly, bioerosion rates are thought to be low in the Paleozoic, but because borings are often forgotten, these rates are potentially incorrect.
Boring allows organisms to no longer be restricted to life on or above sediment and hard surfaces (Warme, 1975). Overlooking these features disregards a relatively large number of species and a lifestyle new to these organisms. Borings also provide important paleoecological information about relationships between organisms. The unique characteristics of borings often allow one to determine whether the host was alive or dead when bored. If the host was living while the borer was active, an interaction between the two may be preserved, and succession of organisms also may become evident. Past habits, lifestyles, and interactions of species are difficult to study because there is little evidence that can be preserved in the fossil record; borings provide an opportunity to collect this type of information.
Ordovician borings occur in a variety of shapes, widths, and lengths, some of which do not conform to those dimensions and forms assigned to Petroxestes, Trypanites, or Ropalonaria. Organismal reactions to borings vary depending on the species being bored, the species of the borer, and the ability of the bored organism to protect itself; determining the reactions may show presently unknown relationships between boring and bored organisms. Because borings from the Ordovician are understood and represented poorly, bioerosion rates for the Paleozoic may higher than assumed.
Answering questions such as the following should help us better understand
the reactions and relationships between the borer and the host in the
Ordovician: Was the organism alive or dead when bored? Were chemical
excretions or other means of self defense used by some species to deter
boring organisms? Could the bored species secrete a new shell or skeleton
after being damaged by borings? Was the bored organism able to grow around
the boring? These questions may be answered from careful microscopic
examination of the specimens as described above.
