Fossils from paleocoastal deposits in northwestern Florida represent at least 3 pleurodire taxa. Biochronologic and paleoclimatic correlates suggest that the presence and absence of side-necked turtles in Florida was synchronous with global climatic shifts in the middle to late Paleogene and early Neogene. The oldest pleurodire record in Florida is from the end of the Greenhouse World in the middle to late Eocene, followed by a hiatus of ∼ 11 million yrs during the onset of the Icehouse World in the early Oligocene. Their sojourn in Florida during the latest Oligocene (25–24 Ma) was concurrent with a brief late Oligocene warming (LOW), and a subsequent hiatus in the early Miocene (∼ 24–18 Ma) was contemporaneous with global cooling. Their resettlement and most populous occurrences in Florida during the middle to late Hemingfordian through early Barstovian (∼ 18–15.5 Ma) coincided with the Middle Miocene Climatic Optimum (MMCO), a significant global warming event. Pleurodires are indicators that paleoclimate in the southeastern United States was frost free during the Eocene, LOW, and MMCO with air and water temperatures warm enough to support these generally cold-intolerant turtles. A small-bodied podocnemidid existed in the Cucaracha Formation (∼ 19.05–18.8 Ma) of Panama during the early Miocene pleurodire hiatus in Florida, and this or a closely related taxon later dispersed into Florida by the early Barstovian, when temperatures were suitable during the MMCO. Previously reported pleurodire fossils from the temporally mixed Lee Creek Mine of North Carolina are most likely middle Miocene in age when pleurodires were common in the Atlantic Coastal Plain of the southeastern United States. The presence of pleurodires in the Seaboard Local Fauna could help constrain the age of the fauna to younger than 18 Ma and probably closer to 17 Ma based on hypothesized paleoclimate at that time. A pleurodire from the middle Eocene Point “A” Dam site in southern Alabama may represent a late occurrence of the Bothremydidae.
Chelonian Conservation and Biology
Vol. 15 • No. 1
Vol. 15 • No. 1
late Oligocene warming
Middle Miocene Climatic Optimum