Biostratigraphy and Paleobiogeography of Eocene Comatulid Crinoids From Florida

Abstract

Fossil comatulid crinoids are reported herein from two localities and stratigraphic units in Florida. This paper is an interpretation of their paleobiogeographic implications and a description of their biostrati graphic distribution. The crinoid Hinierometra bassleri Gislen is present in the Lower Ocala Limestone (Eocene) in west central Florida and a second, unidentified species has been found in the Upper Ocala Limestone (Eocene) of northwestern Florida. The specimens of H. bassleri represent an addition to the geographic distribution of this genus already known from the Eocene of Louisiana and South Carolina in the Gulf and Atlantic Coastal Plains of the United States. Skeletal elements of H. bassleri examined for this study consist of centrodorsals and their associated basal rays and radial plates. The unidentified comatulid specimens from the Upper Ocala Limestone are limited to a singe centrodorsal and several brachia! plate·. Himerometra bassleri occurs with other fossils known to have Tethyan affinities, such as the mollusks Velntes at.cl Nayadina. This association, as well as thP geographic locations of other fossil and modern species of Hinierornetra, supports an interpretation that the distribution of the crinoids is related to circulation patterns of the Tethys Seaway. A paleob;ogeographic shift westward, enabled by the circum-equatorial circulation, resulted in fossil taxa preserved in Atlantic margin areas during the Paleogene; modern taxa, in contrast, have been isolated to the west in the Indo-Pacific region after closure of the Tethys Seaway.