TAXONOMY AND STRATIGRAPHY OF OLIGOPYGUS (ECHINOIDEA) FROM THE EOCENE OF FLORIDA AND GEORGIA

Three easily distinguished species of Oligopygus are recognized in the Ocala Limestone (Priabonian/Jacksonian) of Florida and Georgia. Based upon these taxa, Zachos and Shaak (1978) developed a widely used biostratigraphic zonation that works well in peninsular Florida. However, in the Florida panhandle,Oligopygus haldemani (guide fossil to the Middle Jacksonian) is found in an equivalent of the Oligopygus wetherybyi zone (Late Jacksonian); as evident from both planktic and benthic foraminifera (including Asterocyclina).

The panhandle variety of O. haldemani has been distinguished and named Oligopygus colsoni Lambert, 1932, and is distinguished by the number of pore pairs in the ambulacra. The taxon was treated as a synonym of O. haldemani by Cooke (1959) and Kier (1967) because in all other characters it is similar to that species.

This study quantitatively examined 42 specimens of O. haldemani collected in the Florida panhandle and 148 specimens found in peninsular Florida to determine if there is a significant and consistent difference between O. haldemani from both regions. Specimens were analyzed using four morphological measurements, including number of pore pairs in the first ambulacra. Bivariate plots show that the only significant distinction occurs when pores pairs per ambulacra I are plotted against any of the other measurements (length, width, length of ambulacra I), and even in that character there is ambiguity in assigning single specimens to one form or the other. Principle Component Analysis (PCA) indicates there is a slight difference between specimens from the panhandle and peninsular Florida, but again, much overlap is evident. This difference is not enough to warrant the O. colsoni designation proposed by Lambert because there is considerable overlap between the two morphs. However there should exist, a formal recognition of these two variants for stratigraphic purposes. The evolutionary and biostratigraphic relationships must therefore be reworked to include this slightly different form of O. haldemani.