PALEOBIOGEOGRAPHICAL AND PALEOCLIMATICAL IMPLICATIONS FROM A PERMINERALIZED FRUIT AND SEED FLORA OF THE MIDDLE MIOCENE OF PANAMA

New exposures of the middle Miocene Cucaracha Formation (~17-19.5 Ma) from the Panama Canal provide a unique opportunity to explore ancient biomes that lived in Central America during the Mid Miocene Climatic Optimum. Paleobotanical explorations have yielded a rich deposit of well-preserved permineralized fruits and seeds. Biogeographically these fossil plants document the physical separation of Panama from South America. This Cucaracha flora complements previous paleobotanical investigations of this region, based exclusively on spores and pollen. Disseminules are exposed by breaking the calcium carbonate-permineralized coarse sandstone with a hand-operated screw driven rock splitter. Specimens retrieved by fracturing in this way are investigated in the broken surfaces by light and/or scanning electron microscopy. Families and genera recognized from this carpoflora include Anacardiaceae (Spondias, Pentoperculum), Annonaceae, Arecaceae, Cannabaceae, Chrysobalanaceae (Parinari), Euphorbiaceae, Fabaceae, Humiriaceae (Sacoglottis), Icacinaceae (Phytocreneae tribe), Juglandaceae (Oreomunnea), Lauraceae, Menispermaceae, Myristicaceae, Passifloraceae, and Vitaceae (Cissus). Numerous other fruit and seed types are present, bringing the currently recognized diversity to at least thirty species, compared with 19 documented previously by Alan Graham from pollen. These representatives emphasize the woody component of the flora--mainly trees, shrubs and lianas, whereas the palynological work revealed nine kinds of ferns as well as potentially woody plants (Euphorbiaceae (Alchornea), Juglandaceae (Alfaroa/Oreomunnea), Leguminosae (Crudia), and Rhizophoraceae). The combined floristic data indicate a warm and wet climate during the middle Miocene in Panama, contrary to previous paleoclimatic estimates based on paleosols which suggested very dry and cool conditions during the deposition of the Cucaracha Formation. The presence of annonaceous seeds, Parinari, Sacoglottis, Phytocreneae tribe, and Cissus in the Cucaracha flora and which have also been recorded in the Oligocene-Miocene of northern South America imply that long distance dispersal events across the Panamanian seaway were more common in Neotropical rainforests than thought.