Developing New Techniques in Coprolite Analysis: Packrat Feces from Paisley Caves and Human Coprolites from Hinds Cave

Abstract

The Paisley Caves (35LK3400) are a system of rockshelters in the Summer Lake sub-basin of Oregon. Excavations of these caves resulted in the discovery of 14,300-year-old coprolites yielding ancient human DNA. Pollen analysis from Paisley Cave 2 has produced a record of climate change affecting the Summer Lake Sub-basin during a 7,000-year time period spanning between ~14,500 and 7,600 cal BP. The sediments of the Paisley Caves provide an opportunity to examine questions concerning human-environmental interaction at the end of the Pleistocene Epoch, during the Younger Dryas climatic event. The cave sediments are mixed with abundant, disaggregated, packrat coprolites. A study of pollen records in Cave 2 deposits shows a relatively unchanging environment that combines predominantly xeric conditions with subalpine and marsh communities nearby as well as little evidence of culturally-significant use of any specific plant species. I developed a technique for processing the packrat coprolites. Using this technique, I analyzed fifteen packrat coprolite samples separated from sediments collected from the sidewall of a test unit within Paisley Caves 2. The results were then compared to the previous study based on the fossil pollen in the sediment from the same site. They were similar. However, I found that the packrat coprolites were prone to dietary biases that could mask the true paleovegetation of the area. Methods of processing and sampling human coprolites have changed since the early days of analysis. However, rather than standardizing sampling size and sampling location, practices for collecting material have become specialized by preference and research focus. When sampling a human coprolite for pollen data, sample size and sampling location affect the conclusions of a study. By subsampling five coprolites from Hinds Cave, five times, in five different locations on each coprolite, I was able to compare the pollen ratios from each subsample. I conclude that not only is pollen distribution within a single coprolite heterogeneous, but this lack of homogeneity can result in different interpretations of the coprolites’ contents. These different interpretations can affect conclusions concerning the diets of ancient inhabitants and conclusions concerning the paleoenvironments of the associated archaeological sites.