**This post is the first of several that give additional details regarding some of the different analyses that are currently being conducted with material from Eagle Nest Canyon.**
By Stephen L. Black, Emily R. McCuistion, Matthew E. Larsen, and Chase W. Beck
The 2015 Ancient Southwest Texas Project excavations were the first to document paleofeces (coprolites) in Eagle Cave. During the original site excavations in the 1930s and 1960s no coprolites were reported (even though substantial amounts of paleofeces were likely encountered). Therefore, while not completely unexpected, we were pleasantly surprised when we uncovered the first coprolites.
Extreme care was taken as we excavated these fragile organic remains. Rocket bulb air puffers were used to remove sediment from around in situ specimens. After in-field photography, paleofeces specimens were point provenience with a Total Data Station and/or Structure from Motion (SfM) before being carefully removed and bagged without handling. Specimens were transported to the field laboratory in boxes or by hand to avoid crushing. Temperature extremes were avoided and bags were vented if moisture condensed in the bags.
Preservation conditions of all archaeological material varied across the site. Ironically, the best observed preservation was towards the dripline, whereas the worst was towards the backwall of the shelter. This was true for all non-carbonized organic remains, not just paleofeces. However, even within the well-preserved areas of the site there is differential preservation between individual specimens.
We are still exploring why preservation changes across the site, but some factors affecting preservation became clear when a small sample of coprolites were analyzed in the lab at Texas A&M. Of these, many were fragmentary and exhibited insect bore-holes and vacuoles, suggesting gaseous release before desiccation. Upon microscopic analysis, due to the poor condition of some coprolites the pollen was poorly preserved, and degraded, folded, and torn grains prevented the completion of a standard analysis.
Distribution of Paleofeces
Over 120 coprolites were point-provenienced during the 2015 field season. The majority of these specimens were excavated from the front of the rockshelter and approximately a meter below the surface. At Eagle Cave the coprolites are mainly found in areas of discarded fire-cracked rock and plant remains (cut leaf bases and other fiber). Sometimes they are found within compacted and dry-cracked sediment, which we sampled and hypothesize may be evidence of urine-soaking.
Size is affected by several conditions, including length of time since the last bowel movement and the types of food eaten. Meals based on a single type of food can result in smaller stools, though a vegetarian diet can result in a larger stool than an omnivorous diet.
Previous paleofeces studies have found that plump, shapely coprolites are often from a fiber/plant-heavy meal while the “loose” ones may be from an individual who had recently consumed a lot of meat. There are, however, many other reasons that one could have had fluid bowel movements including parasites, water containing algae-born toxins, plants with a laxative effect (like lechuguilla and sotol), and even an individual’s emotional state.
Color can be indicative of diet; the darker specimens often result from meat consumption while the lighter ones can be indicative of a vegetarian and/or carbohydrate-rich meal. When dried, however, colors change. Nonetheless, it is interesting to note color variations.
Field Lab Observations
Botanists and faunal experts can identify large plant and animal remains within coprolites. Thorough analysis requires rehydrating the coprolite and separating it into constituent parts. Sometimes, however, macrofossils are visible on the surface. In the field lab, Emily McCuistion observed several plant and animal remains while photographing specimens. Observable in the photos to the right are a rather large bone fragment from a jackrabbit-sized creature, as well as numerous seeds, including mesquite and prickly pear.
Ten samples were sent to Texas A&M University for a preliminary study of Eagle Cave paleofeces conducted by Chase Beck. These specimens varied greatly in size, completeness, and preservation. When conducting the analysis of the ten specimens, some contained no coprolitic material, some contained mixed coprolitic and non-coprolitic material and some seemed to be multiple broken piece of coprolites which could not be re-assembeled into a whole.
Five specimens were selected for further analysis. These were hydrated and sieved, and then the material was separated. While the coprolites had some evidence of bone fragments, there was no hair. The majority of material in the coprolites was botanical in nature. Seeds, pollen, calcium oxalate crystals, druse crystals, plant fibers, and phytoliths were all observed. Sotol was the most common pollen grain observed, but other taxa were also present. The presence of calcium oxalate and druse crystals has been linked in the past to the consumption of prickly pear cactus pads. Some of the phytoliths observed are associated with various grass species (Poaceae). The stylus phytoliths are likely sotol (Dasylirion spp.) or agave (Agave spp.). The seeds observed are tentatively identified as sumac (Rhus spp., likely Rhus virens).
Avenues of future analysis include studying macrofossils, pollen, phytoliths, parasites, DNA, radiocarbon dating, and comparison studies with paleofeces from other sites, such as Hinds Cave.
Although the first samples proved too degraded for full analysis, hope remains that DNA may provide more in-depth information. Better preserved samples may be more conducive to future full analysis as well.
The oldest units opened at the end of the 2015 field season are showing some excellent preservation and there are high hopes for more coprolites in the 2016 field season.
A full PDF version of the poster is available here: Blacketal_TAS2015_Paleofeces