Department Seminar: John Southon

Title: The Demise of the Pleistocene Megafauna in the Los Angeles Basin: insights from the La Brea Tar Pits and Lake Elsinore paleo- records

Abstract:15,000 years ago, Los Angeles was home to numerous large mammal species that are now extinct in California, including mammoths, mastodons, dire wolves, saber-tooth cats, American lions, horses, bison, camels and ground sloths. The extinction was continent-wide for all but the bison, and has been attributed to inability to adapt to rapid climate change (specifically the abrupt onset of the Younger Dryas cold period ca. 12,850 years ago) or to human hunting pressure, or both. Effects of various sci-fi catastrophes - supernovae, comet impacts, etc - have also been put forward as the cause, but although those are on the Web they may not be true...

A record of the Pleistocene LA Basin ecosystem is preserved in material trapped in the asphalt deposits of the La Brea Tar Pits, situated within the city of LA itself. Everything from pollen to elephants is preserved, but the record is thoroughly mixed by movement of the trapped material in and with the asphalt, so radiocarbon dating is required to properly locate specimens in time. Our lab has been involved in a project to precisely date the La Brea extinctions and place them in context of other records of changes in the southern California ecosystem, notably those obtained from sediment cores from Lake Elsinore, southeast of LA in Riverside County. The combined results show that the extinctions occurred significantly before the Younger Dryas, in a period where the southern California climate trajectory and ecosystem response seem disturbingly similar to regional changes happening today.