Botanical Preservation in Texas Rockshelters: Eagle Nest Canyon (northeastern Chihuahuan Desert) and McCutchen Branch (Lampasas Cut Plain)

By Leslie Bush, Kevin Hanselka, Christina Nielsen, Daniel Rodriguez, and Carol Macaulay-Jameson

**This is the final post detailing different analyses currently being conducted with Eagle Nest Canyon materials.**

Leslie standing next to her poster at TAS.

Leslie standing next to her poster at TAS.

Abstract

Analysis of botanical samples from rockshelter sites in two different ecological areas of Texas highlight the exceptional value of such sites for paleoethnobotanical research but also the complexities of botanical preservation within and between shelters. In Eagle Nest Canyon, a tributary of the Rio Grande River in the northeastern Chihuahuan Desert, delicate and uncarbonized plant parts such as lechuguilla fibers and bristlegrass chaff are preserved along with the tough, carbonized plant parts that are typically found on open air sites in the area. Preservation does not follow a simple, improving gradient of preservation from the front to the back of the shelters, however. In the more humid climate of central Texas, ancient plant remains at the Barnhill #3 Site (41CV1646) are completely carbonized, or nearly so. Although uncarbonized plant parts are not preserved, the rock shelter provides conditions for the preservation of delicate plant parts such as grass stems and wind-dispersed seeds that are rare to absent on open air sites in the region.

Eagle Nest Canyon

Kelley Cave (41VV164)

Plan map of Kelley Cave showing 2013 excavations and features.

Plan map of Kelley Cave showing 2013 excavations.

Feature 1, identified at the modern surface, consisted of multiple ash lenses with reddened soil at the base. The lack of correlation between bone, debitage, and dung fragments in the Feature 1 level of the cave reflects human digging and rodent turbation (Rodriguez 2015:162). This feature contained less plant material per liter than Feature 6, which was also a burning context.

Feature 4, identified at the surface, dates to roughly 600 cal B.P. It included dense layers of fiber detritus beneath a layer of compacted mud. Sorting and identification of the rich assemblage of plant material in Feature 4 is ongoing, but many leaves and fibers of agave and similar plants and onion bulbs are present. Some carbonized plants are present, but these are mostly wood charcoal and are estimated at ten percent or less of all plant remains.

Feature 6 was encountered at 140 cmbs and dates to roughly 7400 cal. BP.  It is interpreted as a series of overlapping rock-lined pits, with the lower rocks heated in place. No rodent burrows were visible in feature exposures (Rodriguez 2015:126). Insect (termite) and rodent (mouse) feces were recovered in flotation in carbonized form, but the plant remains most likely to represent rodent use (grass and prickly pear seeds) are uncarbonized. It contains more plant material per liter, both carbonized and uncarbonized, than Feature 1.

Summary: The presence of plant remains in particular contexts within Kelley Cave is conditioned both by the types of activities represented (cooking/burning in Features 1 and 6 versus raw plant deposition in Feature 4) and taphonomic processes. Preservation is mostly through carbonization in Features 1 and 6, but a mud drape at the top of Feature 4 led to the preservation of more uncarbonized plant material there. The lower depth of Feature 6 contributed to better plant preservation than in Feature 1 because it afforded better protection from later events such as pit construction and modern looting. The deposition of the mud layer in Feature 4 demonstrates that unique events can produce good preservation of large quantities of uncarbonized plant material at shallow depths in specific locales.

Kelley Macrobot

Eagle Cave (41VV167)

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

PS4. Deposits in this area reflect mixed discard of refuse from cooking, plant processing and possibly other activities. Three samples, including one from feature context (Feature 2) yielded both carbonized and uncarbonized remains of wood, leaves, bulbs, and seeds. Density of several classes of plant remains (wood charcoal, carbonized leaves and bulbs, and uncarbonized seeds) was higher in the feature context than in other samples.

PS3, located at right angles to PS04, is an ash lens that contained carbonized wood, leaves, and bulbs. The sample comes from beneath a heating element, but it is not clear whether that heating event carbonized PS3 plant material. Uncarbonized plants were limited to three fragments of hackberry seeds, which are particularly durable and occur even in pre-Holocene geological deposits (Wang et al. 1997).

Summary: The presence of botanical material in Eagle Cave deposits is conditioned by the type of deposit and taphonomic processes. In PS4 the concentrated focus of human activity represented by Feature 2 produced a greater density of plant remains than other samples in PS4. In PS3, only carbonized plants were preserved, suggesting that uncarbonized plant material succumbed to taphonomic processes that were not operating in PS4 despite the proximity of the two units, possibly due to higher moisture coming from the shelter wall. Interestingly, PS3 is farther from the cave mouth than PS4, indicating that a simple gradient of increasing preservation from dripline to back wall does not apply.

Eagle Macrobot

Eagle Nest Canyon in Regional Context

Two open-air sites in Val Verde County preserve only carbonized plant remains and few small seeds (see chart below and compare to the materials, especially uncarbonized plant parts, in the two charts above). Eagle Nest Canyon samples have these plant remains in abundance and provide unique opportunities to access this part of prehistoric subsistence (see also A Curious Artifact Comes to Light).

Other LPC Sites

 

Yucca seeds from Eagle Cave Feature 2.

Yucca seeds from Eagle Cave Feature 2.

Cord-wrapped bundle as initially exposed.

Cord-wrapped bundle as initially exposed.

Barnhill #3 Rock Shelter (41CV1646)

Plan map of Barnhill #3 Rockshelter.

Plan map of Barnhill #3 Rockshelter.

Twenty-six flotation samples from ten features within the shelter and two off-site samples were examined. In this Central Texas shelter, only carbonized archaeological plant remains survived.

Earth ovens yielded wood charcoal, bulb fragments including camas and wild onion, nutshell (hickory, walnut, and acorn), and 123 small carbonized seeds. A corn kernel fragment was present in one earth oven sample.

Charcoal/ash deposits/middens contained wood charcoal, bulb fragments including wild onion, nutshell (hickory, walnut, pecan, and acorn), and 207 small seeds.

The number of samples analyzed from hearths was smaller, but they included wood charcoal, an unidentifiable bulb fragment, and 59 small, wild seeds.

Only a single pit sample was analyzed. It contained hickory and black walnut nutshell, wood charcoal, and 17 small seeds.

Barnhill Macro

Summary: Plant density at Barnhill #3 is conditioned by feature type, with earth ovens and charcoal/ash deposits/middens having higher botanical density than hearths or the pit feature. Although plant density is higher in the southeastern portion of the site, this seems to be due to the unusual density of charcoal in one sample from Feature 11 (F6-2013; 20.92 g/liter) rather than a true reflection of higher charcoal density in the southeastern area as a whole.

Sunflower (left); Seeds from Barnhill #3 Rock Shelter, scale in mm: vetch from Feature 25 (left-center) and maygrass from Feature 7 (right-center); Wild tobacco (right).

Sunflower (left); Seeds from Barnhill #3 Rock Shelter, scale in mm:
vetch from Feature 25 (left-center) and maygrass from Feature 7 (right-center); Wild tobacco (right).

Barnhill #3 Rock Shelter in Regional Context

Uncarbonized plants do not survive at Barnhill #3 as they do in the Chihuahuan Desert shelters, but the protection of the shelter allows for much better carbonized plant preservation than is usual in limestone regions (Braadbaart 2009). Bulb fragments and, especially, small seeds are present in much higher numbers than on other sites in Coryell County.

Barnhill Regional Context

Conclusion

The presence of plant remains in particular archaeological contexts is conditioned at multiple scales of analysis. Plant samples from the three shelters considered here show several variables in play:

  • regional climate (moisture, soil chemistry),
  • local geology (physical protection of site),
  • activity and intensity of ancient use (thermal events, feature v. non-feature context),
  • taphonomic processes (moisture channels through site deposits, insect and rodent burrowing, looting), and
  • unique events (mud drape on Feature 4).

Acknowledgements

Many thanks to Jack and Wilmuth Skiles and John Barnhill for their good stewardship and site access, and to the Texas Parks and Wildlife Department for use of unpublished data.

**A full PDF is available here: BushEtAl_TAS2015_Macrobotanical_FINAL**

*“Preservation” is used here as a catch-all for the sum total of the processes, natural and cultural, pre- and post- and depositional, that contribute to the presence of plant remains in a particular context.

 

References

Braadbaart, F., I. Poole, and A. A. van Brussel

2009    Preservation Potential of Charcoal in Alkaline Environments: An Experimental Approach and Implications for the Archaeological Record. Journal of Archaeological Science 36: 1672–1679.

Rodriguez, Daniel P.

2015    Patterns in the Use of the Rockshelters of Eagle Nest Canyon, Langtry, Texas. Unpublished M. A. thesis, Department of Anthropology, Texas State University, San Marcos, Texas.

Wang, Yang, A. Hope Jahren, and Ronald Amundson

1997    Potential for 14C Dating of Biogenic Carbonate in Hackberry (Celtis) Endocarps. Quaternary Research 47: 337–343.

References for Coryell County Bulb and Seed Densities

 Bush, Leslie L.

2010    Plant Remains from Site 41CV389, Fort Hood, Coryell County, Texas. Report submitted to SWCA Environmental Consultants, Austin, Texas, February 5, 2010.

2011    Plant Remains from Site 41CV286, Coryell County, Texas. Report submitted to Prewitt and Associates, Inc., Austin, Texas, February 5, 2010.

2015    Plant Remains from 2015 Excavations at Barnhill Rockshelter #3 (41CV1646), Coryell County, Texas. Revised report submitted to Department of Anthropology, Baylor University, Waco, Texas, September 28, 2015.

Thoms, Alston V., Douglas K. Boyd, and Karl Kibler

2015    Earth ovens, Geophytes, and Microfossils: Investigating Burned Rock Features and Archeobotanical Remains on Fort Hood, Central Texas. United States Army Fort Hood Archeological Resource Management Series Research Report No. 65. January 2015.

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Extending Arenosa Shelter’s Reach: Zooarchaeological Research in Eagle Nest Canyon 2015

By Christopher J. Jurgens and Haley E. Rush

**This post is the third of several that give additional details regarding some of the different analyses that are currently being conducted with material from Eagle Nest Canyon.**

Chris and Haley stand in front of their poster at TAS.

Chris and Haley stand in front of their poster at TAS.

Introduction

The Eagle Nest Canyon (ENC) faunal diversity has been significantly less than that found in Arenosa Shelter. Analysis of the faunal remains recovered in 2014 from Eagle Cave and Skiles Shelter has expanded the species diversity from that previously reported. Subsistence remains from the ENC sites show a reliance on deer and rabbits from the canyon and uplands, together with fish from the Rio Grande. Further alteration by bone technology processes similar to Arenosa Shelter is also present in the ENC faunal materials.

Skiles Shelter, site 41VV165 (left), and Eagle Cave, site 41VV167 (right).

Skiles Shelter, site 41VV165 (left), and Eagle Cave, site 41VV167 (right).

Methods and Materials

Analysis methods were similar to those used in the Arenosa Shelter study, with the addition of large mammal bone fragmentation. Differences in teeth, bone, antler, and shell were used to classify animals by taxa. Specimens were identified based on size and visual characteristics of skeletal elements or teeth. Visual characteristics were used to determine age classes.  Cultural modifications to bone were recorded as in the Arenosa Shelter study.  These included disarticulation, skinning, and removal of meat.  Similarly, the degree of burning methodology used in the Arenosa Shelter study was applied to the ENC study with further refinement.  The presence of earth oven deposits in the ENC rock shelters complicated determination of evidence for bone modification through cooking, but different causes for burning were recognized.

Results

Animals Present

To date, analysis of faunal remains has identified 394 fragments surface-collected from Eagle Cave in 2014 and over 300 of the approximately 2,050 fragments excavated from Skiles Shelter in 2014. Twenty three (23) taxonomic assignments have been made for specimens from Eagle Cave, including bison, deer, artiodactyls (deer and/or antelope, turtles (softshells and cooters), rabbit (jackrabbits and cottontails), catfish, bass or sunfish, canids (fox or coyote), rats, undifferentiated small, medium, and large mammals, and undifferentiated small and medium birds.  To date, twenty nine (29) taxonomic assignments have been made for specimens from Skiles Shelter.  More fish taxa are present, as are more small mammals.  Bison is not present in the specimens analyzed at this point.  Hawk remains have been identified.

Taxa Frequency Comparison by Site

Subsistence Remains

Many of the faunal remains present in Eagle Cave and Skiles Shelter have been altered through human subsistence activities.  Skinning, disarticulation, and removal of meat all left distinctive cutmarks on animal bone in the two sites.  Specific types of meat removal indicate filleting of meat from fish, rabbits, or deer, potentially for drying and storage.

Specimen #20031-8, Catostomid Sucker Vertebra with Filleting Damage, Skiles Shelter (41VV165), Excavation Area 1, Unit G, Layer 2

Specimen #20031-8, Catostomid Sucker Vertebra with
Filleting Damage, Skiles Shelter (41VV165),
Excavation Area 1, Unit G, Layer 2

Specimen #20018-59, Jackrabbit Ischium (Pelvis) with Butchering Damage from Dismemberment, Skiles Shelter (41VV165), Excavation Area 1, Unit D, Layer 4

Specimen #20018-59, Jackrabbit Ischium (Pelvis) with Butchering
Damage from Dismemberment, Skiles Shelter (41VV165),
Excavation Area 1, Unit D, Layer 4

Specimen #30020-116, Unprovenienced Deer Ischium Fragment with Butchering Damage from Dismemberment and Filleting. Surface-Collected from Eagle Cave (41VV167)

Specimen #30020-116, Unprovenienced Deer Ischium Fragment with Butchering Damage from Dismemberment and Filleting. Surface-Collected from Eagle Cave (41VV167)

Further fracturing of large mammal bones to remove marrow or to recover fat from the ends left bone fragments of varying sizes.  The intensity of marrow or fat recovery processing is evident from the size of the large mammal bone fragments. Roasting is evident on some specimens. Overall intensive burning (calcination) of some of the bone indicates heat exposure in excess of typical roasting. Much of the burned bone in the sites was discarded and incorporated into earth oven fill.

Bone Burning Pattern Comparison by Site

Large Mammal Bone Fragmentation by Size Class Class 1 = 9 cm

Large Mammal Bone Fragmentation by Size Class
Class 1 = Class 3 = 3-6 cm, Class 4 = 6-9 cm,
Class 5 = >9 cm

Bone Technology Debris

After needs for meat and hides were met, remaining animal bone was sometimes further altered into tools or ornaments.  Using stone tools or flakes, bone was scored, grooved, and snapped to rough shape, then scraped and ground to a final shape.  Remnants of these steps are evident on 35 bone or antler tool fragments or bone manufacturing debris found at the sites during the 2014 field season.

Surface-Collected from Eagle Cave (41VVSpecimen #30025-122, Unprovenienced Spatulate Tool Fragment 167)

Surface-Collected from Eagle Cave (41VVSpecimen #30025-122, Unprovenienced Spatulate Tool Fragment 167)

Acknowledgements

We wish to thank the Skiles family for its long and careful stewardship of the  archeological resources in Eagle Nest Canyon.  We also thank Dr. Steve Black of Texas State University for the opportunity to study zooarchaeological aspects of the sites in Eagle Nest Canyon as part of the Ancient Southwest Texans Project.

 

**A full PDF version of the poster is available here: Jurgens&Rush_TAS2015_Faunal_FINAL

 

References

Gilmore, Zachary

2007  Large Mammal Utilization and Subsistence Stress in Late Prehistoric South Texas. M.A. Thesis, Department of Anthropology, Southern Illinois University. Carbondale, Illinois.

Jurgens, Christopher J.

2005  Zooarcheology and Bone Technology from Arenosa Shelter (41VV99), Lower Pecos Region, Texas.   Unpublished Ph.D. Dissertation, Department of Anthropology, the University of Texas at Austin.  Austin, Texas.

Outram, Alan K.

1998  The Identification and Paleoeconomic Context of Prehistoric Bone Marrow and Grease Exploitation. Unpublished Ph.D. Dissertation, Department of Archaeology, University of Durham.  Durham, U.K.

2001 A New Approach to Identifying Bone Marrow and Grease Exploitation: Why the “Indeterminate” Fragments should not be IgnoredJournal of Archaeological Science. 44(28):401-410.

Rush, Haley E.

2013  The Rowe Valley Site (41WM437): A Study of Toyah Period Subsistence Strategies in Central Texas.  Unpublished M.A. Thesis, Department of Anthropology, Texas State University.  San Marcos, Texas.

 

Micromorph Mania: A Microstratigraphic Approach to Evaluating Site Formation Processes at Eagle Cave

By Christina Nielsen, Charles Frederick, and Ken Lawrence

**This post is the second of several that give additional details regarding some of the different analyses that are currently being conducted with material from Eagle Nest Canyon.**

Tina standing by her poster at TAS.

Tina standing by her poster at TAS.

Eagle Cave (41VV167) is a large dry rockshelter with deeply stratified deposits spanning the Early Archaic through Late Prehistoric periods. My thesis research focuses on deposits in the northern sector of the shelter sampled during 1963 excavations by UT-Austin and again a half century later by Texas State University in 2014. My goal is to use multiple lines of evidence to evaluate the natural and cultural formation processes that resulted in the complexly stratified, culturally rich deposits present in Eagle Cave.

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

Our ongoing analysis involves a robust geoarchaeological sampling strategy that included the collection of micromorphological (micromorph) samples from Profile Sections (PS) 3 and 4 in Eagle Cave. This poster highlights the benefits and difficulties of collecting micromorph samples from fragile rockshelter deposits and shows how the analysis of the resulting slabbed samples and thin sections can aid in evaluating site formation processes.

Profile Section 3 and 4 excavations in Eagle Cave in 2014. Photos taken after initial recordation and sampling, but prior to geoarchaeological sampling.

Profile Section 3 and 4 excavations in Eagle Cave in 2014. Photos taken after initial recordation and sampling, but prior to geoarchaeological sampling.

Methods

Field Collection

  • Section of profile cut back to expose block of matrix
  • Block carefully removed, wrapped in toilet paper, tightly wrapped in tape, and labelled with provenience information,orientation, and north arrow
  • Sample placed in plastic Tupperware or sturdy container
  • Sample impregnated with polyester resin made from polyester, styrene, and methyl ethyl ketone peroxide (MEKP)
Charles Frederick collecting micromorphological samples from PS4 in Eagle Cave in spring 2014.

Charles Frederick collecting micromorphological samples from PS4 in Eagle Cave in spring 2014.

*The micromorph samples were carefully carried out of the canyon and up to Jack Skiles’ shed located a few hundred feet from Eagle Cave. Had the impregnation happened further from the shelter, these friable samples would have been far less successfully embedded.

Dan Rodriguez impregnating micromorphological samples with MEKP in Jack Skiles’ shed.

Dan Rodriguez impregnating micromorphological samples with MEKP in Jack Skiles’ shed.

Slabbing

  • After completely solidified, sample removed from container and north orientation notched in block
  • Outer casing removed using oil-based rock saw to expose intact soil block
  • Each side of block is scanned using high resolution
  • Block is cut into 1cm slabs for thin section production, curation, and macroscopic analysis
  • 4 x 6cm sections cut from slabs to be sent to Spectrum Petrographics, Inc. to be made into thin section slide

 Sampling

The sampling strategy was fairly simple: capture as many stratigraphic layers (strats) as possible within the PS3 and PS4 profiles. As archaeological and geoarchaeological sampling had already occurred prior to the micromorph collection, some strats identified during the initial profile recordation were no longer visible in the profile.

Summary of Micromorphological Samples from PS3 and PS4 in Eagle Cave

Summary of Micromorphological Samples from PS3 and PS4 in Eagle Cave

Specific types of strats that were especially important to capture in the micromorphs included microstratigraphy such as thin lamina and lenses as well as strats that were associated with cultural features. Using this strategy, the 13 relevant micromorph samples captured approximately 27 of the 85 total stratigraphic layers identified in the field. A total of 22 thin section slides were made then from the 13 micromorph samples.

Micromorph sample MM1 from PS3A (FN 30744). This micromorph slab was cut into three 4 x 6 cm blocks to be sent off and made into thin section slides (denoted by red boxes). The three sections were numbered FN 30744-1 through 30744-3. High resolution scans of each of the resulting thins section slides are presented on the right. Thin section analysis is currently underway.

Micromorph sample MM1 from PS3A (FN 30744). This micromorph slab was cut into three 4 x 6 cm blocks to be sent off and made into thin section slides (denoted by red boxes). The three sections were numbered FN 30744-1 through 30744-3. High resolution scans of each of the resulting thins section slides are presented on the right. Thin section analysis is currently underway.

Thin section slide 30744-1 from PS3A. This thin section correlates to strat S40 and S41. S40 was initially recorded as a light gray ash deposit and S41 was characterized as a thin, white ash lens. From the micromorph block and thin section, you can see that these deposits look far different from how they appeared in profile. S40 has a fairly dense concentration of charcoal as well as fragments of shell and rock

Thin section slide 30744-1 from PS3A.
This thin section correlates to strat S40 and S41. S40 was initially recorded as a light gray ash deposit and S41 was characterized as a thin, white ash lens. From the micromorph block and thin section, you can see that these deposits look far different from how they appeared in profile. S40 has a fairly dense concentration of charcoal as well as fragments of shell and rock

Thin section slide 30744-2 from PS3A. This thin section contains the lower boundary of strat S42 and S43. S43, was also recorded as an “ashy” layer, but does not appear so in thin section. Similar to S40, numerous charcoal and rock fragments are visible in thin section.

Thin section slide 30744-2 from PS3A.
This thin section contains the lower boundary of strat S42 and S43. S43, was also recorded as an “ashy” layer, but does not appear so in thin section. Similar to S40, numerous charcoal and rock fragments are visible in thin section.

Thin section slide 30744-3 from PS3A. This thin section possibly correlates to strat S51, which was recorded as an animal burrow. In thin section, this looks very similar to S43 and may have been misidentified during micromorph collection. S51 may have been completely removed during initial sampling. Additional analysis needs to be done to identify whether post-depositional processes are present.

Thin section slide 30744-3 from PS3A.
This thin section possibly correlates to strat S51, which was recorded as an animal burrow. In thin section, this looks very similar to S43 and may have been misidentified during micromorph collection. S51 may have been completely removed during initial sampling. Additional analysis needs to be done to identify whether post-depositional processes are present.

 

 

Benefits

The deposits in Eagle Cave, like many other Lower Pecos rockshelters, are very dry and have a loose consistency. This posed many challenges during initial recordation of strats and with the subsequent geoarchaeological sampling. Profile Section walls became enveloped in a film of dust with the slightest breeze or movement. Despite efforts to clean walls prior to all documentation, observations during strat recording were somewhat hindered by the persistent dust. The collection and analysis of micromorph samples, however, allows for a clearer examination of stratigraphy and the relationships between various deposits. Characteristics that aid in deciphering formations processes, such as boundaries between strats, are especially difficult to determine when obstructed by dust. Thin sections made from the micromorph samples can provide information crucial to the study of formations processes such as the size, orientation, sorting, and mineral composition of grains, organics, and artifacts as well as post-depositional disturbances of sediments.

Challenges

Since the micromorph samples in PS3 and PS4 were collected after all other sampling had been completed, it was sometimes difficult to correlate the samples with the strats initially identified in the field. In hindsight, ideally the micromorph samples should have been collected immediately after the strats were identified and documented to allow for a more accurate correlation.

Field collection is also not always successful in loose deposits such as these and many first (and second) attempts at collection failed. Patience and perseverance are necessary qualities to have in this type of setting. The entire micromorph process, from collection to analysis, is a lengthy one but the potential information that can be obtained from this type of analysis greatly outweighs the challenges you may face along the way.

Left: Annotated SfM image of PS3A depicting stratigraphic layers identified during initial recordation; Right: Micromorph block MM1 ready to be removed from profile PS3A. MM1 collected from area where strats S40-42 and S51 were initially recorded, but as you can see, the strats do not quite look like how they did prior to sampling. Note: In situ, many of the strats look like ash deposits. However, as you can see from the MM1 block these “ashy” deposits are not in fact ash, but have a dark-colored matrix with large quantities of rock, charcoal, and other inclusions. The dusty field conditions make it difficult to characterize the strats with a high level of accuracy during initial recording.

Left: Annotated SfM image of PS3A depicting stratigraphic layers identified during initial recordation; Right: Micromorph block MM1 ready to be removed from profile PS3A. MM1 collected from area where strats S40-42 and S51 were initially recorded, but as you can see, the strats do not quite look like how they did prior to sampling.
Note: In situ, many of the strats look like ash deposits. However, as you can see from the MM1 block these “ashy” deposits are not in fact ash, but have a dark-colored matrix with large quantities of rock, charcoal, and other inclusions. The dusty field conditions make it difficult to characterize the strats with a high level of accuracy during initial recording.

Conclusion

Long inhabited limestone rockshelters with deeply stratified deposits, such as Eagle Cave, can be difficult for an archaeologist to interpret. The natural degradation of the shelter itself, combined with human modification and natural forces create often complicated stratigraphic deposits. My thesis research involves a multidisciplinary approach to evaluate the formation processes evident in PS 3 and 4. The ongoing analysis of the micromorph slabs and thin sections from this sector of the shelter will help elucidate some of these complex processes and contribute to the overall analysis of formation processes in this sector of the shelter.

**A PDF version of this poster is available here: Nielsen_Micromorphs_TAS2015_FINAL

Paleofeces at Eagle Cave: A Preliminary Report of Ongoing Research

Paleofeces at Eagle Cave: A Preliminary Report of Ongoing Research

**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.**

Steve Black stands next to the coprolite poster at TAS.

Steve Black stands next to the coprolite poster at TAS.

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.

(Left) Paleofeces in association with faunal remains. (Center) Emily McCuistion using a rocket bulb to gently poof sediment away from a coprolite. (Right) Coprolite on a rock in situ. Another is visible in the profile.

(Left) Paleofeces in association with faunal remains. (Center) Emily McCuistion using a rocket bulb to gently poof sediment away from a coprolite. (Right) Coprolite on a rock in situ. Another is visible in the profile.

Preservation

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.

There are distinctive differences between a well-preserved coprolite (top) and a poorly preserved coprolite (bottom).

There are distinctive differences between a well-preserved coprolite (top) and a poorly preserved coprolite (bottom).

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.

Locations of point-provenienced paleofeces samples from Eagle Cave.

Locations of point-provenienced paleofeces samples from Eagle Cave.

Paleofeces Variation

A representative sample of Eagle Cave coprolite sizes, colors, forms, and preservation states. All coprolites are displayed to scale.

A representative sample of Eagle Cave coprolite sizes, colors, forms, and preservation states. All coprolites are displayed to scale.

SIZE

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.

SHAPE

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

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.

Preliminary Analysis

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.

Macrofossils observed in Eagle Cave coprolites. Clockwise from top-left: a mesquite endocarp in a coprolite fragment; jackrabbit-sized bone embedded in a coprolite; and unidentified seeds in a coprolite.

Macrofossils observed in Eagle Cave coprolites. Clockwise from top-left: a mesquite endocarp in a coprolite fragment; jackrabbit-sized bone embedded in a coprolite; and unidentified seeds in a coprolite.

Laboratory Analysis

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.

Microfossils observed in Eagle Cave coprolites (from left): unknown Liliaceae phytolith; sotol phytolith; and an unidentified phytolith.

Microfossils observed in Eagle Cave coprolites (from left): unknown Liliaceae phytolith; sotol phytolith; and an unidentified phytolith.

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).

Microfossils observed in Eagle Cave coprolites (from top): calcium oxalate crystals found abundantly in prickly pear cactus; stylus phytolith indicative of lechuguilla or sotol; and raphide crystals common in both sotol and lechuguilla.

Microfossils observed in Eagle Cave coprolites (from top): calcium oxalate crystals found abundantly in prickly pear cactus; stylus phytolith indicative of lechuguilla or sotol; and raphide crystals common in both sotol and lechuguilla.

Future Study

Matthew Larsen uses sign language to indicate he has discovered another coprolite.

Matthew Larsen uses sign language to indicate he has discovered another coprolite.

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