RECLASSIFICATION OF A COMMON CALYMENID TRILOBITE FROM SILURIAN CARBONATE DEPOSITS OF SOUTHWESTERN OHIO

As previously reported, the most common trilobite in the Silurian carbonates of Ohio – especially the Springfield Dolomite – is a species that has been assigned to at least four genera over the past 100 years. This trilobite has been variously referred to as Calymene celebra, Flexicalyemene celebra, Gravicalymene celebra, and Sthenarocalymene celebra. Reexamination of sp. celebra through parsimony and morphometric analysis, in conjunction with stratigraphic correlation, is being used properly place this calymenid species within the correct genus.

Previous studies have shown that the lower Silurian bedrock deposits of Southwestern Ohio can be correlated worldwide. A eustatic transgression during the Wenlockian, and subsequent slow shallowing are responsible for the alternating carbonate and clastic deposition found in the carbonate bedrock. The Springfield Dolomite is indicative of this shallowing event.

In the past 75 years, the pioneers of trilobite research have labored extensively to classify the family Calymenadaie. A major study by Shirley in 1936 attempted to classify the calymenids on the basis of cephalon characteristics – specifically the shape of the glabella, variations in the preglabellar field, and the development of papillate lobes – feeling that other morphological characteristics were conservative at best, and unreliable. Subsequent studies have followed Shirley's proposed classifications based upon these characters within reason.

Recent advances in morphometric analysis have aided in the systematic revision of organisms. The graphing of outline shapes as x.y coordinates, as well as Principal Components Analysis using Procrustes fitting and Elliptic Fourier shape analysis places sp. celebra initially within the genera Calymene, Metacalymene, Sthenarocalymene, and to a lessor degree, Flexicalymene. Stratagraphic correlation removes the possibility of Sthenarocalymene. Parsimony analysis, utilizing much of Shirley's work from 1936, further correlates sp. celebra within a proper genus, Calymene, as initially described by Raymond in 1916.