A Comparative Analysis of Wet and Dry Ashing Techniques for the Extraction of Phytoliths from Plant Material

Two methods are commonly used for the extraction of phytoliths from plant material to be used as reference in the analysis of archaeological phytolith samples: (1) spodograms or dry ashings; and (2) acid digestions or wet ashing. It has been suggested that these techniques may modify the resultant samples in different ways. Dry ashing, in particular, has been implicated as a cause of shrinkage and warping in phytolith assemblages when incineration occurs at ≥450°C. The results of a morphometric comparative analysis between the dry ashing and wet ashing methods do not support these claims. This study establishes that differences in patterns of dimension and curvature of short bilobate phytoliths and of elongate phytoliths both subjected to dry and wet ash preparation are not statistically significant. There is, therefore, no detectable evidence of morphological impact as a result of these methods. This finding implies that any differences that do occur in phytolith size and curvature are typical, possibly random permutation within assemblages, or that they are the result of variation in leaf cell structure rather than the consequence of a particular extraction procedure. This suggests that the practice of using different methods of preparation of reference samples for fossil analysis can be reliably continued.     

TAPHONOMIC OBSERVATIONS OF ARCHAEOLOGICAL WHEAT PHYTOLITHS FROM NEOLITHIC ÇATALHÖYÜK,TURKEY, AND THE USE OF CONJOINED PHYTOLITH SIZE AS AN INDICATOR OF WATER AVAILABILITY*

An investigation of wheat husk phytoliths from a midden deposit at Neolithic Çatalhöyük provided the opportunity to investigate the impact of taphonomic processes on conjoined phytolith size. Wheat husk phytoliths from a possible crop processing deposit were examined using three methods. The results indicate that the size of conjoined forms decreases significantly as a result of laboratory extraction and slide preparation. Observations of the phytolith layer in thin section show some of the depositional and post‐depositional processes affecting phytolith size. These results indicate that these taphonomic factors need further investigation before conjoined phytolith size can be used to infer past water availability and agricultural practices.     

Phytoliths and microcharcoal at Jinluojia archeological site in middle reaches of Yangtze River indicative of paleoclimate and human activity during the last 3000 years

A variety of phytoliths, together with prolific microcharcoal particles, sponge spicules and diatoms were extracted and identified in four cultural layers from an archeological site at Jinluojia, Macheng, Hubei Province, Central China. The warmth (Iw) and aridity (Iph) indices calculated from grass phytoliths reveal warm and wet periods during the West Zhou, early East Zhou, Tang and Song Dynasties whilst cool and dry periods occurred during the late East Zhou, Ming and Qing Dynasties. The paleoclimate conditions reconstructed on the basis of grass phytoliths extracted from archeological sediments are in agreement with those from natural sediments in the Middle Yangtze region. In contrast, the woody phytoliths show a positive correlation with microcharcoal particles, suggesting an anthropogenic contribution to the woody phytoliths from the use of woody plants for fuel during cooking and heating. Two episodes of the enhanced abundance of woody phytoliths and microcharcoal particles were found to occur at East Zhou Dynasty and from Ming and Qing Dynasties to the Present, proposed to be a consequence of the population expansion and/or the frequent wars.     

A Comparison of Three Methods for the Extraction of Phytoliths from Sediments

This paper compares three methods commonly used to extract fossil phytoliths from sediments. A basic procedure using heavy liquid flotation and oxidation is compared with two other procedures across a range of sediment types commonly encountered in archaeological studies. The three procedures are: (1) a heavy liquid flotation method (HLF); (2) a burning method (POW); and (3) another heavy liquid flotation method (HLFPol) similar to HLF, but adapted to allow the extraction of pollen and spores as well as phytoliths, within a single process. Comparisons of the resulting output using these three techniques for phytolith extraction show that different methods can produce different results, and therefore basic techniques should be modified according to the characteristics of the sediments for which they are used. While all the techniques showed similarities in assemblage results, there were problems associated with disaggregation and effective separation of light and heavy fractions, in particular with the POW procedure. The evidence suggests that morphotype selection occurred both within the physical sorting process and in the process of inverting slides to shed excess residue; in both cases it is difficult to suggest a solution to the problem. The results show clearly that the advantages gained by using the POW procedure are largely outweighed by the problems encountered with its use, and because of possible size/shape selection, it is not recommended for general extraction procedures. The heavy liquid flotation procedures, on the other hand, are shown to produce more concentrated residues with higher levels of clarity and less potential than the POW procedure for sample bias. The use of a non-toxic heavy liquid, sodium polytungstate, now allows the process to be used in relative safety. It is recommended that analysts use heavy liquid flotation procedures with chemical treatments specific to sediment requirements.     

Phytolith identification criteria for foxtail and broomcorn millets: a new approach to calculating crop ratios

Broomcorn and Foxtail millets were major crops in the Yellow River Valley region, Henan, China, during the Neolithic Yangshao period. Phytoliths and macro remains have been used to understand crop choices in this period. Distinguishing between phytoliths from millet crops and panicoid non cultigens can be challenging. We examine the effect of using only one or two identification criteria compared with a more stringent five or more with phytoliths from archaeological samples to examine crop ratios. We compare our results with the results from the macro remains. This demonstrates, firstly, that using more identification markers has a very definite effect on the results and secondly, phytoliths and macro remains are complementary proxies that when used together can produce more accurate results than used alone.     

Dental wash: a problematic method for extracting microfossils from teeth

A variety of microfossils, originating from plant foods, become trapped in the dental calculus matrix. Processing of dental calculus allows extraction of these microfossils. The resulting data can be used to reconstruct diet at the individual and population levels as the identification of microfossils like starch grains and phytoliths to the generic level, and sometimes to the species level, is possible. However, in some archaeological sites, dental calculus deposits do not preserve well enough to be processed. To prevent the loss of information in such cases, we present a technique, called “dental wash”. It permits extracting microfossils from cryptic dental calculus deposits. In the two experimental archaeological cases presented herein we identified phytoliths, starch grains as well as a diatom fragment with this method, whereas in a control sample no microfossils were found. Moderate damage to the teeth was detected when they were already friable due to poor preservation. Minor damage to the surface of well-preserved teeth was observed. This indicates that the proposed method is efficient in recovering microfossils, but unacceptable because of damage to teeth. If the method can be refined, it will expand the potential of dental calculus analysis to a greater range of archeological sites.     

The phytolith archaeological record: strengths and weaknesses evaluated based on a quantitative modern reference collection from Greece

The phytolith record from archaeological strata is a powerful tool for reconstructing aspects of past human behaviour and ecology. Considerable insights into the problems and potentials of this record can be obtained by studying phytoliths in modern plants. We prepared a phytolith reference collection of modern plants mostly from northern Greece that includes quantitative information on phytolith concentrations (number of phytoliths per gram dry organic material) and morphological assemblages. Here we analyse this reference collection with the aim of evaluating the strengths and weaknesses of the archaeological phytolith record. The reference collection comprises 62 different plant taxa. Of them, 28 are trees, 1 conifer, 10 shrubs and 1 herb, 3 domesticated annual legumes and 19 monocotyledons. We demonstrate quantitatively the extent to which woody species, legumes and fruits of dicots contribute only small amounts of phytoliths to the sediments per unit tissue dry weight, while leaves of trees and shrubs produce significant amounts of phytoliths and grasses are prolific phytolith producers. We compare the data of this reference collection with a similar reference collection from another Mediterranean ecosystem (Israel). The comparison indicates that some aspects of phytolith production are probably genetically controlled, whereas others are environmentally controlled. We note that despite the fact that woody species produce few phytoliths per gram of tissue, their record can be most informative when taking into account other properties of the sediments. We also note that jigsaw puzzle-shaped phytoliths normally form in plants that grow in humid conditions, but may form in arid environments when the plants are irrigated. This study clearly shows the extent to which some plants can be under-represented and others over-represented in the phytolith record. Knowing the extent of this bias can greatly improve our interpretation of the phytolith record.     

Investigating crop processing using phytolith analysis: the example of rice and millets

The application of crop processing models to macro-botanical assemblages has traditionally been used to interpret past husbandry practices and organisation of labour involved in crop-processing. Phytoliths offer an alternative method of analysis because they are durable in most environments, regardless of whether plant parts are charred, and the identification of plant types and plant parts allows them to be used in much the same way as macro-botanical remains. Indeed macro-remains and phytoliths are complementary datasets for examining the input of plant parts, such as crop-processing waste, into archaeological deposits. We outline crop-processing models in relation to macro-remains and then develop the framework for their application to archaeological phytolith assemblages. Rice and millet processing models are explored in relation to patterns expected in both macro-remains and phytoliths. The utility of these models is demonstrated with archaeological evidence from the site of Mahagara, an early farming site in North-Central India. The results indicate a way to employ phytoliths in archaeology which complements the fragmentary evidence available from plant macroremains.     

One,two, three phytoliths: assessing the minimum phytolith sum for archaeological studies

The number of phytolith studies has increased steadily in the last decades in palaeoecological as well as archaeological research, and phytolith analysis is currently recognised as a proper area of expertise within archaeobotany. This has led towards a strengthening in the standardisation of the different steps involved in analysis; e.g. sampling strategies, laboratory extraction or processing of plant material/soils for the creation of reference collections. In spite of this, counting procedures remain one of the areas that could be further developed. The aim of this paper is to assess representativeness of phytolith count size in archaeological samples and specifically to assess whether an increase in total number of individuals counted influences the number or distribution of morphotypes observed. Two statistical tests are performed to evaluate the representativeness of count size: phytolith sum variability analysis (PSVA) and morphotype accumulation curve (MAC). The analyses show the relationship among the number of counted phytoliths, the variability (that is, the number of different morphotypes identified) and the stabilisations of the MACs. Results allow us to support the standard count size in phytolith studies, which ranges from 250 to 300 particles. Together with a quick scan, this strategy should produce a precise and clear phytolith assemblage for archaeological studies.     

Phytolith assaying using a micron-scale electrokinetic sorting ring

A particularly useful indicator of past vegetation are phytoliths, glassy products of plant metabolism which have distinctive size and morphology based on the plant taxa which produced them; however, their analysis is a time-consuming task. Building on investigations into mobilizing and sorting of synthetic polystyrene microspheres using a closed loop rectangular microelectromechanical systems (MEMS) electrokinetic array, we investigate these devices’ utility for sorting natural microparticles. Using phytolith samples extracted from archaeological sediment, we show that closed loop MEMS can separate the glassy bodies from both mineral contaminants and each other. Also, small differences in polarization between the phytoliths cause lateral segregation between particles of different sizes and shapes. This process facilitates manual analysis by providing a motive force to the phytoliths that translates and rotates them, showing different configurations as they are propelled by the MEMS array. The organization of the phytoliths into streams also opens the door to automated analysis using image processing. Phytolith assaying is therefore feasible using a MEMS electrokinetic ring and merits additional research to explore the potential of this innovative approach.     

A simple preparation technique for the study of opal phytoliths from archaeological and quaternary sediments

This note describes a simple and inexpensive method for the extraction and counting of opal phytoliths from archaeological and Quaternary sediments.     

Experimental assessment of maize phytolith and starch taphonomy in carbonized cooking residues

Many taphonomic studies of plant microfossils, specifically phytoliths and starch, are concerned with post-depositional movement, contamination, and morphological changes due to environmental fluctuations or plant processing. Additionally, the identification of phytoliths and starches archaeologically are based on their presence or absence. This paper examines whether it is possible to identify maize (Zea mays ssp. mays) phytolith and starch abundance associated with different processing behaviors as replicated through experimentally produced cooking residues. If successful, identification of likely associated processing and taphonomy of these microfossils will allow for a more refined interpretation of plant use as it relates to timing and plant form and processing.     

Morphometric distinction between bilobate phytoliths from <Emphasis Type="Italic">Panicum miliaceum</Emphasis> and <Emphasis Type="Italic">Setaria italica</Emphasis> leaves

The development of identification criteria for crop plants based on phytoliths is of high relevance for archaeology, palaeoecology and plant systematics. While identification criteria are available for major food crops, these are mostly based on phytoliths from inflorescences, while other plant parts remain undetected. This paper focuses on bilobate phytoliths from leaves of Panicum miliaceum L. (common millet) and Setaria italica (L.) P. Beauv. (foxtail millet), two taxa that co-occur in regions of Asia and Europe since prehistory and regularly occur at archaeological sites in Eurasia. Leaves of the investigated taxa were systematically sampled to explore the variation of short cells and to collect 27 morphometric variables of bilobate phytoliths with newly developed open-source software. The data was analysed by discriminant analysis, analysis of variance and multiple comparison tests. The resulting morphometric data from five populations per species enables a distinction between the bilobate phytoliths of P. miliaceum and S. italica. Observed differences between populations within species affect only few parameters. This possibility to classify populations of bilobate phytoliths from P. miliaceum and S. italica leaves offers a new method for the detection and identification of these taxa in archaeology, amongst others.     

Evaluating the usefulness of phytoliths and starch grains found on survey artifacts

Archaeologists use survey artifacts to study any number of interesting topics. The focus of this study is to test the usefulness of starch grains and phytoliths found on artifacts recovered during archaeological survey. Phytolith and starch grain analysis was used to determine the level of environmental contamination on three types of medieval ceramics collected during survey work from plowed fields in the parish of Wicken, Northamptonshire, England. The plant residues found on these artifacts were compared with their surrounding soil and with contemporaneous excavated artifacts recovered from under the floorboards of a medieval house in nearby Wyton, Cambridgeshire, England. Through the use of the “piggyback” approach pioneered by Chandler-Ezell and Pearsall, phytoliths and starch grains were systematically removed from the artifacts surface. Residues associated with contamination were removed from the outermost layer of the artifact surface while potentially uncontaminated residues were removed from the innermost layer of the artifact surface. Matching phytoliths and starch grains were found on the outermost surface of the survey artifacts and in the surrounding soils. No phytoliths and starch grains were found on the innermost surface of the survey artifacts suggesting that residues from the surrounding soils did not penetrate into the pores and crevices of the artifacts. The overall results suggest that, although they are preliminary, there is potential for plant residue analysis of survey artifacts.     

The extraction and identification of opal phytoliths from the teeth of ungulates

A method is described for the extraction and identification of opal phytoliths from food residue on the teeth of cattle. Two types of residual food debris were recognized. These yielded varying quantities of silica particles from plants and soil. The application of the identification of silica bodies to enviromental archaeolory is discussed.     

Extended depth of focus image for phytolith analysis

This paper proposes a new phytolith analysis method by extended depth of focus technology. The extended depth of focus image is sharp throughout by the image processing of a series of photos, while each acquisition of the original photo will be compromised and show certain parts of the specimen in and out of focus. Consequently, the extended depth of focus image is suitable for computer-assisted morphometrics analysis. Meanwhile, the extended depth of focus image can be used for three-dimensional reconstruction images. Experiments on rice husk multi-cell panel show that the three-dimensional reconstruction image method can reconstruct multiple double-peaked phytoliths at one time. We also measure the parameters of multiple double-peaked phytoliths from the reconstructed three-dimension image. Comparative experiments show that the reconstructed three-dimensional image is precise enough for rice identification. Based on the above experiments, we recommend the extended depth of focus method as a promising tool in phytolith research.     

Experimental patterns of hammerstone percussion damage on bones: implications for inferences of carcass processing by humans

The common occurrence of hammerstone percussion damage (pits, striae, notches and impact flakes) on the fossil limb bones of ungulates indicates that marrow extraction has been an important component of hominid butchery for over two million years. Beyond this level of basic inference, it would be behaviorally informative if three deeper aspects of marrow harvesting were understood more clearly: (1) whether inter-element patterns of bone fragmentation vary when processing intensity is held constant; (2) whether butcher investment in marrow extraction correlates positively with the number of percussion marks generated; (3) whether taphonomic effectors can be identified based on percussion mark morphology, frequency and placement. Some experimental work has been conducted previously in service of exploring these questions, but we set out here to address them explicitly through the analysis of a large sample of white-tailed deer (Odocoileus virginianus) limb elements fractured by hammerstone percussion. Our results indicate that (1) measures of bone fragmentation, which supposedly reflect processing intensity, are highly contingent on the research question being posed. This stresses the fact that researchers must be explicit in their definition of processing intensity. (2) In addition, hypothesized covariance between number of hammerstone blows and percussion mark frequencies are not met in our sample, corroborating previous conclusions of a lack of covariance between cutting strokes and cutmark frequencies. These results highlight the contingent nature of butchery mark production, and emphasize the need to investigate carcass resource exploitation by posing questions that do not rely on mark frequencies, but instead utilize other zooarchaeological measures. (3) Finally, our results—showing high incidences of impact notches and flakes created by direct anvil contact and “anvil scratches” created by direct hammerstone contact—suggest caution in using specific categories of percussion damage to infer their taphonomic effectors.     

Do silica phytoliths really wear mammalian teeth?

There is considerable literature suggesting that silica (opal) phytoliths cause dental enamel microwear in mammals. Much of this literature cites a single study from 1959 as evidence that silica phytoliths are harder than mammalian tooth enamel and so have the potential to cause dental microwear. No other studies using similar methodology have actually confirmed whether phytoliths are harder than dental enamel.     

Stability of phytoliths in the archaeological record: a dissolution study of modern and fossil phytoliths

Opaline phytoliths are important microfossils used in archaeological and ecological research. Relatively little is known about the stability of phytoliths after burial. Under alkaline pH conditions they can dissolve, and mechanical disturbances can cause a loss of their more delicate appendages. Here we present an experimental study of phytolith stability (combination of solubility and abrasion). Modern and fossil phytoliths were extracted from wheat using new methods to minimize dissolution, and by burning in an oven. These assemblages were placed in a solution buffered to pH 10 and maintained under constant temperature and shaking conditions. The silicon concentrations in the solution were monitored once a week for 5 weeks. The phytolith morphologies in each assemblage were determined at the outset of the experiment and after 5 weeks. The results show that there are differences in stability between various assemblages. Modern inflorescence wheat phytolith assemblages are more unstable than those from leaves/stems. Burnt assemblages are less stable than unburnt assemblages, and a fossil phytolith assemblage about 3000 years old is more stable than the modern wheat assemblages. The results also show that individual phytolith morphotypes have different stabilities, and as a result of dissolution and abrasion, some morphotypes may resemble others. This study further shows that archaeological and/or paleo-environmental interpretation of phytolith assemblages may change with the assemblage’s state of preservation.     

Microarchaeology of a collective burial: cova des Pas (Minorca)

FTIR and phytolith analyses have been used to understand the exceptional preservation of the organic remains at the burial cave of Cova des Pas (Minorca), and to obtain high-resolution data of the plant remains present in the sediments. The presence of sodium nitrate and gypsum suggests a relatively dry environment that has enabled the preservation of the organic material, and contributed to the natural mummification. The dry conditions also favored phytolith preservation. Grass inflorescence phytoliths are abundant all over the site suggesting that phytolith accumulations might have an anthropogenic origin and are related to the burial ritual.