EXCEPTIONAL PRESERVATION AND CONCENTRATION OF WHOLE-BODY RANILIA (DECAPODA: RANINIDAE) IN THE PLIOCENE INTRACOASTAL FORMATION OF FLORIDA

In Liberty County, Florida over 500, nearly complete to complete, carapaces of a new species of Ranilia, were collected from the Pliocene Intracoastal Formation. The low degree of disarticulation of the crabs indicates that they were buried rapidly, most likely during a severe storm event(s). At least six other decapod genera occur in association with the Ranilia but all were much less abundant (and still await study). The Intracoastal Formation, first described by P. Huddlestun in 1976, is primarily a subsurface unit, occasionally cropping out along streams and riverbanks from western-most Okaloosa County eastward to southwestern Wakulla County. However, recent excavations in Liberty County exposed nearly five meters of section; the upper three meters dominated by Ranilia fossils. The crab-bearing unit is a slightly phosphatic, loosely cemented, carbonate sand, easily removed by precipitation. At several locations in the quarry, Ranilia carapace density averaged six per square meter. Given that the quarry is approximately 0.3 kilometer square and that the Ranilia fossils occur throughout the quarry wherever the Intracoastal Formation is exposed, rough estimates indicate that many thousands of Ranilia carapaces may have been present prior to mining. Previous reports of Florida Pliocene crabs, made by Rathbun (1935), are limited to Petrochirus bouvieri Rathbun, 1918, Menippe nodifrons Stimpson, 1859, and Parthenope charlottensis Rathbun, 1935, and were based solely on chelae and fingers. Bishop and Portell (1989) described the first Florida Pliocene whole-body crab, Petrolisthes myakkensis, thus the total known species diversity of Florida Pliocene crabs (prior to this report) was a meager four.