I had the opportunity contribute to two articles for a special issue of Quaternary International entitled "Not Only Use" that was edited by Juan Luis Fernández-Marchena, Lena Asryan, Antonella Pedergnana, and Andreu Ollé. The issue contains an impressive overview various methodologies used to study wear the burgeoning interest in multidisciplinary efforts to study wear traces (i.e., traceology) of different origins and the processes (i.e., operative chains) involved in manufacture, use, and abandonment of an object that is later recovered by an archaeologist (check out the editorial by Fernández-Marchena et al. for more info). The first article was lead by Raquel Hernando. In short, Hernando was interested in understanding if recent advances in optical microscopy could resurrect its use for the study of human dental microwear. Hernando noted that dental microwear analyses originally used optical microscopy, but it was later replaced by scanning electron microscopy (SEM). Eventually confocal microscopy became the favored technology for occlusal dental microwear analysis (i.e., dental microwear texture analysis, or "DMTA"), while SEM is still preferred for buccal microwear analysis. However, Hernando and colleagues note that SEM analyses are costly (we generally pay by the hour to use these microscopes) and the postprocessing of images is also quite time consuming (and exhausting for your eyes!). DMTA is generally quicker, but the microscopes—and software needed for DMTA—is not nearly as widely accessible as SEM. That means costly travel, lodging, and user fees to do DMTA analyses for many of us without local access to equipment. So, why not revisit optical microscopy? Hernando and colleagues point to many advances in optical microscopy that have been explored in the context of traceology. Buccal microwear seemed like the best place to start since it still widely uses SEM. Hernando and colleagues found that OM produces very similar results to traditional SEM methods whether one studies the original tooth or a dental cast of a tooth (see image below). Above: Comparison of scanning electron (SEM) and optical microscopy (OM) images of buccal microwear. Note the excellent resolution in OM. Raquel Hernando and colleagues noted that optical microscopy provides many other advantages over traditional SEM analysis: less expensive equipment with less associated maintenance, wider accessibility of optical microscopes for researchers, less eye fatigue, greater image resolution, 3D appearance of images with greater definition, and relatively quick data acquisition and analysis. A drawback is the need to build up open-access databases for comparitive purposes, but the data produced in this paper marks the beginning of that effort. This study points out the importance of revisiting methodologies with a critical eye, but also how interdisciplinary research—something IPHES takes great pride in—can lead to innovation in allied fields of research. The second article explored the use of gigapixel-like (GPL) images for studying external surfaces of teeth. GPL images make use focus-stacking (extended focus images) and panoramic stitching of microscopic images to create mosaic images with high depth of field using SEM. This “gigapixel-like” (GPL) imaging strategy can be used to create multiscale, high-resolution images of entire, or partial, dental surfaces that can be viewed from a field of view that encompasses an entire tooth surface to high magnification views of dental microstructure, microwear, taphonomic features, among other features. The images have a variety of uses from the communication of results in scientific publications to their use in interactice museum displays and websites or training researchers. Above: simplified outline of focus-stacking and creation of image mosaic to create a gigapixel-like (GPL) image. Above: A GPL image (center) with call-out boxes of varying magnification that indicate different surface features. Descriptions proceed clockwise from upper right corner. Orange rectangle: Medium size antemortem enamel chip with well-worn margins. Green rectangle: Detail of cementoenamel junction and root surface. Subtle perikymata (bottom left quadrant) and striations (upper left quadrant) are visible on the enamel. Subtle postmortem cracking of root surface also evident. Magenta rectangle: Detail of furrow-form hypoplasia with clearly visible perikymata (between white arrows). Black arrow points to dental calculus deposit. White rectangle: Detail of instrumental striation with a right oblique orientation. Blue rectangle: arrows indicate microstriations on labioincisal edge and a well-worn, but small, antemortem enamel chip to the left of the image. While the goal of the publication was to outline the GPL methodology and uses, we also made an interesting discovery from the creation of a GPL image for one of the teeth from the Chalcolithic context (dated to about 4000 years before present) of El Mirador Cave near Burgos, Spain. We found that at least one tooth exhibited a strange discoloration when viewed with the naked eye (see photo below). Microscopic examination revealed that the discoloration is related to enamel erosion—something that is rarely documented in prehistoric contexts. Above: Photo of original tooth with discolored (yellowish) enamel surface. GPL image sampling indicated by black box and GPL image indicated by orange arrow. Zooming in on section 300x shows "honey-comb" appearance of enamel surface. This indicates erosion of the enamel. This study makes me suspect that erosion in teeth from archaeological contexts is much higher than we currently acknowledge, and calls for a need for detailed analyses of the original teeth in conjunction with high magnification analysis for definitive diagnosis. Nonetheless, this is a very interesting (and rather accidental) discovery. More analyses of the El Mirador material are underway. References and further reading These studies:
Additional references:
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Dental microwear analysis is a tried-and-true method of reconstructing the diets of living and extinct animals – including early hominins and Homo sapiens – from prehistory to the present day. Microwear can be thought of as the microscopic “pits” and “scratches” that form on the tooth surfaces as food is chewed. The foods we consume, the ways foods are processed and prepared, and the particles that are ingested with food (e.g., dust and grit from the environment, particles worn off grindstones or milling devices, etc.) all influence the microscopic wear patterns on tooth surfaces. Microwear ”texture” is a way of quantifying wear in three-dimensions using standardized variables that reflect the directionality, size, depth, and other characteristics of enamel microwear (see the example below). Thus, microwear variation by group or individual can reveal a great deal of information concerning diet and past human lifeways. Photosimulations (left) and 3D representations of microwear textures. wear. The top two are from a Natufian forager, the middle two are from a Roman-era farmer from Herculaneum, and the bottom two are from a Mongolian pastoralist. The dark colors are low points and the hot (white/red) are higher points. Contemporary culinary traditions are vast, but prehistoric and historic diets also varied incredibly. In a pre-globalized world, eating local and less mechanically processed foods would have been the norm, local environmental conditions would have had an extensive influence on the types of foods available, and cultural practices would dictate how those foods were prepared. So, the grains, fruits, vegetables, tubers, meat and anything else you can think of stuffing down your gullet are only part of what influences microwear signatures on teeth. Other aspects to consider are whether these foods are wild or domestic, raw or cooked, grilled or boiled, salted or fermented, and so on and so on... One way of teasing out these influences on microwear signatures in archaeological contexts is through the creation of large comparative databases that include human groups with extensive spatial, temporal, environmental, and cultural variation – variation that would, in turn, also influence dietary variability. This is exactly what Christopher Schmidt (University of Indianapolis) and a team of 24 researchers set out to do using a global sample of 719 individuals from 51 archaeological sites (see map below). Locations of groups sampled in the study. Details of chronology, archaeology, subsistence, and more can be found in the original article. Schmidt and colleagues tested three main hypotheses to better understand the utility of microwear texture analysis for paleodietary reconstruction. We (yep, I was a co-author in the study), lumped the individuals studied into 3 general subsistence categories: 450 farmers, 192 foragers, and 77 pastoralists. Foragers gather, hunt, and/or fish for their sustenance; primarily consume non-domesticated foods; and generally process foods to a lesser degree than farming and pastoralist groups. Farmers tend to consume a diet dominated by domesticated plants, most frequently grains; and frequently use more intensive food processing (milling, grinding, boiling, etc.) than foragers which contributes to softer diets. Pastoralists are typically very mobile people relying on animal husbandry. Dietary staples such as cheese, meat, and yogurt are consumed but frequently supplemented with grains. Thus, pastoralists diets are generally soft with some abrasive content. However, these categories are NOT hard-and-fast distinctions. Instead, subsistence variation within these categories is HIGHLY variable, but broad categories allowed us to test for broad differences between groups. We found that important differences are found between the “big three” subsistence categories (see figure below). However, there were also interesting differences between foragers and farmers in the New World and Old World as well as interesting differences through time in the Old World farmers. Scatter Plot with the mean (central point) and standard deviations (lines) of the two microwear variables analyzed in the study. Some broad differences can be seen but the substantial overlap in subsistence groups can also be seen. Without getting into too much detail about the finer differences acknowledged in the study, I’d rather come back to the initial point I made about variability within the macro-categories we are using. Keep in mind that each comparative sample is unique because of the circumstances in which those people lived – e.g., local climate, environments, food availability, and the culinary traditions they practiced among other factors. However, each group also has its own internal variability related to things like age, sex, social status, etc. All of this variation is bound to make for extremely interesting case studies as the human groups in this study are are re-analyzed and published as individual case studies. Aside from being very happy to participate in this study, I am really looking forward to the individual papers that my co-authors will be preparing on the samples they contributed here.
Full Article: Schmidt CW, Remy A, Van Sessen R, Willman J, Krueger K, Scott R, Mahoney P, Beach J, McKinley J, d’Anastasio R, Chiu LW, Buzon M, De Gregory R, Sheridan SG, Eng J, Watson J, Klaus H, Da-Gloria P, Wilson J, Stone A, Sereno P, Droke J, Perash R, Stojanowski C. Herrmann, N. Dental microwear texture analysis of Homo sapiens sapiens: Foragers, farmers, and pastoralists. American Journal of Physical Anthropology, 169(2), 207-226, https://doi.org/10.1002/ajpa.23815. If you’re interested in other research on prehistoric diets, I strongly urge you to get a hold of one of these popular accounts by Peter S. Ungar: The Real Paleo Diet. Scientific American, 319(1), 42-49. Evolution's Bite A Story of Teeth, Diet, and Human Origins https://press.princeton.edu/titles/10943.html |
John C. Willman
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