Antibodies, Antigens, and Bear: Residue Analysis from a Middle Woodland Encampment
Archaeologists from Rummel, Klepper & Kahl, LLP (RK&K) conducted investigations at the Adelphi Site (18PR1024), a short-term Middle Woodland encampment (circa AD 850) in Beltsville, MD, on behalf of the Maryland Department of Transportation State Highway Administration for the Intercounty Connector Project. Fourier Transform Infrared Spectroscopy (FTIR) and crossover immunoelectrophoresis (CIEP) were utilized on artifact samples from the site to provide additional insights on the foodways of the site’s inhabitants.
Typically, an article about a prehistoric archaeological site will focus on typological analysis of artifacts. The artifacts certainly do provide significant information to aid in interpreting a site. However, specialized analysis of the artifacts can offer nuanced and detailed information about the site’s inhabitants. Twelve select artifacts from the Adelphi Site were submitted for residue testing to determine what plants or animals may have been utilized on the site. FTIR was used on three ceramic sherds to test for organic residues and CIEP was used to test nine stone tools for animal proteins. Here’s what we knew about the site before those tests were completed.
Located on a poorly drained floodplain, it is thought the site was occupied temporarily during the late summer or fall dry season, enroute to or from larger encampments. Inhabitants repaired and replaced stone tools and cooked using ceramic pots over a central hearth. The recovery of Mockley ceramics (Figure 1) and Jack’s Reef Pentagonal projectile points (Figure 2) made of non-local jasper suggest the occupants were likely part of a larger Middle Woodland community.
Figure 1. Mockley Ceramic with Swamp Potato Root Residue
Figure 2. Jack's Reef Corner-Notched Point with black bear residue
The three ceramic sherds were submitted for FTIR analysis to test for residues of the foods cooked in them. The FTIR process involves soaking the artifacts in a solvent of chloroform and methanol (CHM) which absorbs organic residues present on the artifact’s surface. The CHM solvent is allowed to evaporate, and the captured residues from the artifact are then placed in the path of infrared radiation beams which pass through the residue samples. By measuring the infrared wavelengths, a Fourier Transform Infrared Spectrometer converts the measured wavelengths to data which can be compared to an existing reference library of measurement data and match the wavelengths to known organic residues.
Using FTIR, the three ceramic sherds tested positive for residues of Sagittaria (Wapato, Swamp Potato) root. Other residues were present but not in sufficient quantities to be recognizable. Sagittaria is an edible tuber that is widespread across North America and is found in shallow waters and swamps and may have been present on-site at the time of occupation.
Nine stone tools were submitted for CIEP residue analysis to test for the presence of animal proteins. CIEP is based on an antigen-antibody reaction and can be used to identify organic materials (antigens) present on tested artifacts. Antigen residues present on artifacts are removed in a “chemical bath” similar to the methods used in FTIR. The solution breaks down the bonds which allow proteins to adhere to the artifact. Soundwaves can also be introduced to the process to further loosen the protein bonds. Once any proteins are separated from the artifact, they are placed within a gel and introduced to known antisera (a blood serum containing antibodies) and electrophoresed. In a positive reaction the proteins and antisera will create a visible line in the gel between the two samples.
A Jack’s Reef Corner-Notched projectile point (Figure 2) from the site tested positive for black bear residue and a second Jack’s Reef projectile point tested positive for American eel residue. The negative results for the seven other samples may be the result of insufficient protein residues or a lack of use. The latter could be indicative of a new unused tool, or one discarded during manufacture due to failure – it broke before being finished. A tool may also have had any residues removed if the edges were resharpened after use. Given the amount of late-stage reduction present in the tool-stone workshops documented on site, these are all plausible theories.
How did these results contribute to the interpretation of the Adelphi Site? They offer information into the diet of Middle Woodland people at small encampments and provide insight to what attracted the occupants to the wetlands and banks of Paint Branch and Little Paint Branch--an environment suitable for Wapato and American eel harvest. The black bear residue on the point could be the result of a recent successful hunt either near the site or prior to arrival.