EXCEPTIONAL PRESERVATION IN CENOZOIC ECHINODERMS FROM FLORIDA

Echinoderms are well-known from many formations in Florida, but their degree of articulation and preservation may vary significantly from one unit to another both spatially and temporally. Asteroids typically disarticulate into isolated ossicles upon death, yet the only assemblage of articulated individuals of Heliaster (sun stars) recorded is from the Pliocene in southwestern Florida. Similarly, Cenozoic ophiuroids are not normally preserved as complete individuals. However, close examination of fossil seagrass from the Florida Eocene reveals that intact brittle stars can be found as distinct molds in rare circumstances.

Echinoids generally preserve better than other Cenozoic echinoderms because their tests consist of fused plates of calcite that resist disarticulation upon death. Only the radioles tend to be removed and dispersed as taphonomic processes proceed. Echinoderms (including echinoids) also tend to resist chemical alteration of the high Mg calcite plates via replacement, recrystallization, or dissolution. Examples of unusually well-preserved echinoids have been collected from formations such as the Ocala Limestone (Eocene), Marianna and Suwannee limestones (Oligocene), Chattahoochee Formation (Miocene), Peace River Formation (Mio-Pliocene), and the Tamiami and Intracoastal formations (Pliocene). These well-preserved echinoids include internal molds (dolomitic) in which microstructures of skeletal plates remain, and even recrystallized echinoid tests. Several examples of exceptional preservation also exist for infaunal irregular and epifaunal regular echinoids in the younger Tamiami and Intracoastal formations (Pliocene) from the southern and northern regions of the state (respectively). In fact, some of these relatively fragile echinoids still have radioles articulated to the tubercules (including select brissids and Eucidaris specimens), and this is highly unusual for echinoids in Florida.