A Late Miocene occurrence of the extinct salamander Batrachosauroides (Caudata, Batrachosauroididae) and other new caudate fossils from Florida and Georgia, USA

Abstract

Two partial vertebrae of the rare, large-bodied, aquatic salamander Batrachosauroides are reported from the Upper Miocene Love Bone Bed (late Clarendonian, ~10–9 Ma) Alachua County, Florida. They represent the latest occurrence of Batrachosauroides by 2.8–5.8 million years from previous records and are the latest account of the family Batrachosauroididae in the eastern United States, being either younger than or approximately coeval with fossils of Peratosauroides problematica from the Clarendonian San Pablo Formation of central California. While most Neogene Batrachosauroides in North America are from the warm interval spanning the Late Oligocene Warming (LOW) to the Middle Miocene Climatic Optimum (MMCO), this is the first unequivocal account well after the conclusion of the MMCO suggesting Florida was a post-MMCO refugium during global cooling in the Late Miocene. Batrachosauroides vertebrae from the late Hemingfordian Suwannee Springs site (Florida) and the late Barstovian Gragg Mine (southwestern Georgia) are also described. Two other caudate taxa are present at the Love Bone Bed, Ambystoma and a mid-sized Siren that is the most common amphibian in the Love Bone Bed Local Fauna. The presence and rarity of Ambystoma further corroborates the existence of peripheral or seasonal lentic aquatic habitats adjacent to the main lotic body of the Love Bone Bed deposit. Other salamanders from the paleocoastal Gragg Mine Local Fauna include Notophthalmus and Amphiuma n. sp., aff. Amphiuma pholeter. The latter represents the oldest record of the A. pholeter lineage and documents its presence in the Gulf Coastal Plain since the Middle Miocene. The Gragg Mine represents a unique interval in the southeast at the conclusion of the MMCO.