EOCENE DISPERSAL OF THE ECHINOID GENUS ECHINOCYAMUS IN THE SOUTHEASTERN UNITED STATES

Seven species of the tiny (less than 10mm length) clypeasteroid echinoid Echinocyamus have been described from the Eocene deposits of the western hemisphere: three can be shown to be conspecific with E. parvus, and the remaining species should be assigned to other genera. Echinocyamus parvus is shown to occur in a narrow chronostratigraphic range, which correlates closely with the deposition of the Gosport Sand in southern Alabama and the Bartonian/Priabonian transition. The sudden, isolated appearance of the genus is evidence of an exotic source (probably Africa) and the rapid dispersal of the species from North Carolina through Georgia and into Alabama is evidence for short-term reversal of the ocean current flowing through the Suwannee Channel. Stressful environmental conditions may have caused deviant reproductive adaptation in the species, and eventually led to the disappearance of the genus from North America until the late Oligocene.