Late Pleistocene Megafaunal Deposits on the Isthmus of Panama and Their Paleoenvironmental Implications

Abstract

Two megafaunal deposits were discovered next to the villages of La Trinidaita and Llano Hato during an archaeological survey on the Azuero Peninsula of Panama. The fossil sites were found near other localities first reported in 1957 by Smithsonian paleontologist Lewis Gazin. Bones at La Trinidaita and Llano Hato rested in tight horizontal clusters at the bottom of ancient creeks and ponds. The remains appear to have been buried rapidly by thick deposits of fine clay when environmental conditions were wetter and cooler than today. Animals identified at La Trinidaita and Llano Hato include Cuvieronius tropicus, Eremo- therium sp., and some turtles. Radiocarbon-dated charcoal fragments associated with the bones gave con- temporaneous dates of 44,840 ± 700 and 47,040 ± 900 14 C yr B.P. These dates indicate that carcasses accumu- lated during the Marine Isotope Stage 3 (MIS3) interstadial. Because other fossils were not found above or below these principal deposits, it is argued that the MIS3 environment was especially favorable for sup- porting large browsers and mixed-feeders and preserving their bones on the landscape. These environmental and taphonomical characteristics likely disappeared as the climate of the lowland Neotropics became drier in response to the following arid glacial advance. During this time, C4 plants dominated the landscape and may have forced gomphotheres and giant ground sloths to abandon the dry Pacific lowlands and follow the rising tree-lines. Such large-scale range re-organization may have caused animals to abandon some regions of lower Central America during the Last Glacial Maximum.