Site: Olorgesailie Species: H. erectus Year of Discovery: 2003  Discovered by: A team led by Richard Potts  Geological Age: About 900,000 years old  Cultural Attribution: Acheulean  Developmental Age: Presumed Sex:
Preserved Skeletal Party: Frontal bone, including the brow ridge  Preservation: Partial  Preservation Details: Anatomical Description: Additional Notes:
Source: Encyclopedia of Human Evolution and Prehistory: Second Edition]
Early to Late Pleistocene locality, dated 1.2 – 0.05 Ma, in the rift valley of southern Kenya known for concentrations of Acheulean handaxes and Middle Pleistocene fauna. The Olorgesailie Formation represents lake-margin and fluvial environments preserving a series of open sites. Dense accumulations of Acheulean handaxes occur in the middle part of the formation, ca 780 Ka. Tools in several of these strata are associated with rich fossil accumulations of the extinct gelada Theropithecus oswaldi. The handaxe sites occur closest to the central axis of old stream channels. According to excavations by Potts in the 1980s and 1990s, both kinds of site were deposited on the same ancient landscape and reflect spatial variants of behavior of the same toolmakers.
Olorgesailie documents a characteristic suite of Pleistocene large mammals, including the last-known occurrences of taxa such as Elephas recki and Hipparion, important in Early and Middle Pleistocene faunas. Once thought to encompass a brief time interval, Olorgesailie actually represents a long span calibrated by argon-argon (Ar/Ar) dating, including a revised upper Jaramillo paleomagnetic boundary (992 Ka) and the Brunhes/Matuyama boundary (780 Ka). Research has documented strong shifts in lake size and chemistry indicative of intensified paleoclimatic and tectonic activity during the Middle Pleistocene.