Monday 2 April 2018

Dating the Middle Stone Age-Later Stone Age transition at the Kisese II Rockshelter in Tanzania.

The Middle Stone Age of Africa is lasted from around 280 000 years ago to between 50 and 25 000 years ago. It is associated with the Levallois technology, in which the chips derived from a central core are themselves used as cutting tools, which the core is retained as a source of material rather than being used as a tool in itself, and with both anatomically Modern Humans and some archaic forms. The Later Stone Age, which replaced this, is a associated with a range of more sophisticated technologies, particularly the development of larger blades by removing numerous chips from a central core, as well as other forms of sophisticated behaviour such as bead-making and cave painting. This transition is thought to have begun in East Africa, making that area of great interest to palaeoanthropologists, however, despite a large number of sites in the region spanning this transition, reliable chronologies have been established for very few of these, making the timing of the transition hard to decipher.

In a paper published in the journal PLoS One on 28 February 2018, Christian Tryon of the Department of Anthropology and Peabody Museum of Archaeology and Ethnology at Harvard University, Jason Lewis of the Turkana Basin Institute and Department of Anthropology at Stony Brook University, Kathryn Ranhorn, also of the Department of Anthropology and Peabody Museum of Archaeology and Ethnology at Harvard University, Amandus Kwekason of the National Museum of Tanzania, Bridget Alex of the Department of Human Evolutionary Biology and Peabody Museum of Archaeology and Ethnology at Harvard University, Myra Laird of the Department of Organismal Biology and Anatomy at University of Chicago, Curtis Marean of the Institute of Human Origins at Arizona State University and the African Center for Coastal Palaeoscience at Nelson Mandela Universty, Elizabeth Niespolo of the Department of Earth and Planetary Science at the University of California, Berkeley, and the Berkeley Geochronology Center, Joelle Nivens of the Center for the Study of Human Origins at New York University, and Audax Mabulla, also of the National Museum of Tanzania, examine the chronology of the Kisese II Rockshelter in the Dodoma Region of Tanzania.

The Kisese II Rockshelter forms part of the UNESCO World Heritage Kondoa Rock-Art Sites, a collection of over 150 rock shelters on the eastern slopes of the Masai escarpment bordering the Great Rift Valley, noted for their exceptional rock art, much of which dates from the Late Pleistocene. The site was first explored in 1935 by Louis and Mary Leakey documented the site's paintings. The Leakeys returned to the site in 1951 when they began the first of a series of archaeological digs at the shelter. This exploration was taken over by Raymond Inskeep in 1956, who dug down to a depth of 6 m at the site, recovering a wide range of fossil specimens, over 5900 lithic objects (stone tools) and a huge number of Ostrich-shell beads and ceramic fragments, as well as seven Human burials and some iron slag. However Inskeep published little data on the site, and switched his attention to sites in South Africa before the end of the 1950s. He did return to Kiseses II in the 1980s, but abandoned the project after his notes were stolen. Tyron et al. returned to the site in 2011 and began fresh excavations, as well as seeking out Inskeep's material for re-evaluation.

Rock art at Kisese II. Schematic representation of a portion of the painted rock face at Kisese II, redrawn from Mary Leakey. Tyron et al. (2018).

Tyron et al. built up a chronology for the Kisese II Rockshelter using radiocarbon dating of Ostrich-shell beads and fossil remains, as a way of dating lithic artefacts from the same sedimentary layers, with a view to understanding cultural changes in the Late Pleistocene at the site. The oldest artefacts were found to date from about 46 200 years ago, while the youngest were only about 4500 years old.

Archaeologists at the Kisese II Rockshelter in 2015. Christian Tyron in Tyron et al. (2018).

Tyron et al. found that Ostrich-shell beads were present  at Kisese II, from around 38 000 years ago, while traces of red ochre, a dye made from the mineral hematite (Fe₂O₃), and frequently used as a pigment in both rock and body art by both ancient and modern populations, were found to date to about 43 000 years ago. Stone tools are found in the earliest deposits at Kisese II; and persist till the end of the sequence. Many of these fragments cannot be assigned to any particular lithic culture, but artifacts assignable to the Middle Stone Age Levallois Culture being present in deposits dating from the earliest part of the sequence to about 35 000 years ago, and Later Stone Age Blades first appearing about 36 000 years ago, and persisting till the end of the sequence.

Ostrich eggshell beads, bead blanks, and production debris from Kisese II, showing diversity of production methods. Tyron et al. (2018).

This presents a rather more complicated chronology at Kisese II than is generally envisaged. Rather than Middle Stone Age technology being replaced by Later Stone Age tools, beads and decorations, the site was first occupied by people using Middle Stone Age tools, who then adopted the use of ochre, followed by beads, followed by Later Stone Age tools, before eventually abandoning Middle Stone Age tools. However, this too might be an oversimplification of the situation, as all of the Later Stone Age technologies are known from other sites in East Africa that predate the oldest deposits at Kisese II, which suggests an alternative possibility, that the technologies were always available, but were not adopted at Kisese II because they were not needed by the local population.

See also...
Follow Sciency Thoughts on Facebook.