RETROGRADE COMMUNITY STRUCTURE IN THE LATE EOCENE OF ANTARCTICA

Current paleobiological models hold that predators eliminated populati ons of epifaunal suspension feeders from shallow, soft-substrate marin e environments beginning in the Mesozoic. Among the suspension feeders affected were dense populations of ophiuroids, which are rare in shal low water today, and isocrinid crinoids, which today occur only in the deep sea, The La Meseta Formation on Seymour Island, Antarctic Penins ula, represents an ecological anomaly: this deposit contains localized , autochthonous, dense assemblages of ophiuroids and isocrinids in a l ate Eocene, shallow-water setting, The rare occurrence of sublethal ar m injuries in both the ophiuroid and crinoid populations suggests low predation levels, as seen in similar populations before the Mesozoic. Sporadic return to a Paleozoic community structure was apparently prov oked by changes in temperature and productivity in Antarctica during t he late Eocene.