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10.1: Introduction to Reconstructing Environments and Subsistence Patterns

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    To understand and interpret past human behavior, archaeologists need a complete understanding of the past natural environment and regional climate at a site. Reconstructing the environment and climate allows archaeologists to identify the plants and animals with which humans shared the landscape and examine how humans at the time adapted in response to the resources available to them. This chapter reviews a few of the ways archaeologists can use data to reconstruct the environment and climate at the time a site was occupied and identify food resources in terms of the flora (plants) and fauna (animals) that would have been available to the site’s occupants.

    Sedimentology, which analyzes how sediments were deposited at a site in the past, is one of the tools archaeologists use to analyze past environments and climates. The size and shape of deposits and the texture, size, and shape of the material they contain all give archaeologists clues about how the sediment ended up at a particular location. For example, a glossy, rounded sediment that’s relatively small in size was likely carried a long distance by water before being deposited. Scattered fields of rocks and other debris of various sizes and shapes, on the other hand, point to transportation by a glacier.

    In terms of flora, tree rings can provide useful information about regional variations in climate, particularly in terms of the amount of rainfall at the time. For many types of trees, each ring in a cross-section of the trunk identifies one year of growth with widest rings during unusually wet years and thinnest rings during severe drought years. Individual tree species respond differently to climatic conditions and thus provide somewhat different data. Archaeologists trained in dendrochronology can “read” the tree ring data and obtain information about the climate that existed when the rings were created, including changes in the climate over time.

    Other large plant remains, called macrobotanicals, are also useful in reconstructing environments. Archaeologists can identify plant species at a site even when they are no longer present from imprints left behind by seeds and fruits in sediment and from charcoal left behind from burning wood in a fire pit. Reconstructing the environment helps determine whether plants found at a site were native to the area or likely came from another region and environment, indicating travel and/or trading relationships. And by examining the associations between macrobotanical remains and other artifacts, we gain information about how the plants were used by humans in the past.

    Small microbotanical remains include items such as pollen grains, which are microscopic, and small seed and plant structures. They are often abundant in archaeological sites but are not always studied because collection requires fine screening techniques such as water flotation. Palynology refers to the study of pollen grains, which has been an integral part of archaeology since the early twentieth century. Their size, shape, and structure can be used to identify the genus of plant that produced the grains. Like all organic matter, pollen grains are best preserved in dry environments such as caves and in anaerobic conditions such as those found in peat bogs.

    Pollen is collected using a tool similar to an auger probe. Archaeologists extract long vertical cores of soil and sediment and examine carefully measured segments of the cores under a microscope to view and identify the pollen. Sometimes a more-involved chemical process is needed to remove the pollen grains from the matrix. In that case, the task is turned over to a palynologist. Once the grains are visible, each type of pollen in the sample is identified (typically at the genus level only) and counted. The results can be presented graphically to show how plant species present at the site changed over time or during its occupation.

    Phytoliths are another type of microbotanical remains. They are minute particles of silica (silica also makes up sand) from plant cells that can survive long after all other parts of a plant, including pollen, decompose. Plants produce these particles in large quantities, and phytoliths are commonly found in the remnants of hearths, in layers of ash, inside pottery that contained plants at one time, and wedged in the crevices of animal teeth. Phytoliths can, in many cases, identify plants at the genus and species level and are used to confirm pollen sequences determined from core samples.

    Diatoms are a type of plant microfossil that consist of single-celled algae found in water that have silica cell walls instead of the cellulose cell walls found in plants. Thus, like phytoliths, diatoms survive long after cellulose plants decompose. Diatoms have been studied for more than 200 years, and many varieties, each with a unique structure, have been identified and classified. Their well-defined shapes allow archaeologists to identify the specific diatoms uncovered at a site, and the assemblage of diatoms present can be used to answer questions about the salinity (salts), alkalinity (bases), and nutrient content of the water in which they formed.

    When archaeologists study animal (fauna) remains at a site, they are particularly interested in how the animals wound up there—whether they were raised there by occupants, were wild and occurred naturally at the site, or were brought there by the occupants or by predators. Generally, large animal remains (macrofauna) are not as useful to archaeologists when reconstructing an environment as small animal remains (microfauna). Animals such as deer, buffalo, and boars often occupy large territories that shift with changes in the environment. Small animals such as rodents, bats, and other insectivores tend to be associated with localized geographic features such as caves and swamps. Burrowing animals present a challenge, however, because remains found at a site could represent animals present when the site was occupied or animals that burrowed down to that location hundreds or thousands of years later.

    Another example of microfauna remains that can be useful in reconstructing an environment is owl pellets—something you might have dissected in school. The pellets are the regurgitated remains of the owl’s meal, consisting of the bones, teeth, claws, and fur that they cannot digest. Owls do not travel far when hunting so their pellets provide a snapshot of the microfauna available at the time within a radius of just a few kilometers.

    Remains of birds and of land and marine mollusks (snails) are also good indicators of climate change and the local environment. Both species are generally fairly well preserved, and the particular species present reflect the local climate. Birds, for example, occupy different types of climates in terms of annual average temperature and the presence or lack of fresh and salt water. Archaeologists compare modern species of mollusks and the habitats they prefer with changes in the percentage of various marine mollusks in the past to reveal interesting information about shifts in coastal micro-climates that determine whether a shore is rocky or sandy.

    Whatever type of animal species archaeologists study when reconstructing a past landscape, it is important not to rely on a single species indicator. Basing a reconstruction solely on the calcium carbonate of land mollusks, for example, would likely miss important details represented by other animal remains at the site.

    In addition to climates and natural environments, archaeologists reconstruct the diets of those who occupied a site using plant and animal remains. It is important to realize that there is a big difference between a meal and a diet. A meal is a single event—your dinner last night, for example. From an archaeological perspective, it is nearly impossible to reconstruct a single event at a site. That kind of information typically comes from analyses of fecal matter, stomach contents, and written records. Diet, on the other hand, is the long-term pattern of consumption and represents the types of foods eaten on a regular basis. Many lines of evidence are used to reconstruct the diet of a culture. Zooarchaeology is the study of animal bones, and paleoethnobotany is the study of past uses of plants. However, as noted earlier, archaeologists have to understand the preservation of the site and its taphonomy (study of what happens to archaeological remains after burial or deposition) to determine whether the archaeological materials in question were brought to the site and consumed by humans or wound up in the archaeological record in another way.

    When trying to reconstruct diet using macrobotanical remains, archaeologists need a large sample size. One cannot conclude anything about diet from the presence of one peach pit or one grape seed; in fact, from such scant evidence, it is not clear whether the fruit was eaten at all, let alone whether it was a regular part of a human’s diet. When using pollen data, archaeologists must collect a minimum of 100 grams of pollen of a species before they can clearly determine the plant’s importance in a diet.

    Whatever types of plant remains are recovered, it is important to quantify the remains by weight and number and arrange them graphically by abundance much in the same way palynological pollen data is presented when reconstructing a past landscape. Plant remains are both weighed and counted because either method alone would favor certain types of plants over others.

    It is important to reconstruct diets not only for hunter-gatherers and other prehistoric groups but also for more-recent agricultural groups. An analysis of chemical residues such as proteins, fatty acids, and DNA can be used for simple identifications of plants in agricultural settings. Residues found on artifacts such as stone sickles (phytoliths) used to harvest wheat, for example, can confirm that the occupants engaged in harvesting practices. The study of processes of domestication of wild species is also important in archaeology. Sometimes the transition from wild to domestic is fairly easy to see archaeologically, such as morphological changes in a plant’s structure (e.g., the transition from maize to the corn cob we know today is obvious).

    When analyzing animal remains for their role in a people’s diet, archaeologists have to take several factors into account. One is how the animal ended up at the site. Another important consideration is whether the animal was eaten or was used for some other purpose, such as providing milk or antlers, horns, and skins for tools and clothing. To determine if the animal was used for food, archaeologists look for marks on bones that indicate that a human scraped meat from the bone with a tool or cut the bones versus marks of predators gnawing on the carcass and etching of the bones by plants. A scanning electron microscope can examine the bones for minute signs of wear. Human-made tools typically leave V-shaped marks while gnawing of carnivores leaves more rounded marks.

    When trying to make sense of animal remains at an archaeological site, some basic data are collected and tabulated before they are examined more thoroughly. Often the first step is to identify the species, if possible. Then, the remains are quantified to determine both how many pieces of bone there are and the likely number of individuals the remains represent. The raw count of pieces of bone is the number of identified specimens (NISP). So, say, twelve femurs from ancient cattle. The minimum number of individuals (MNI) accounts for how many individual animals can be represented by the number of specimens. Consider the twelve femurs from cattle. If four of the specimens are right femurs and eight are left femurs, the MNI (minimum number) is four since each cow had only one right femur. Archaeologists also calculate the meat weight provided by an individual specimen, which varies with the age and sex of the animal and the season in which it died.

    After collecting basic quantitative data about bones at a site, archaeologists study other aspects of the remains, such as the sexes and likely ages of the animals, which can provide clues about whether the animals were wild or domesticated. Methods for determining the age and sex of animals from bones are similar to ones used with human skeletons. Like humans, male and female animals have different pelvic structures. Archaeologists also look at teeth, horns, and antlers since female deer species do not have antlers and male carnivores typically have larger canine teeth. They also examine the eruption and amount of wear on teeth and how developed long bones such as femurs are, which points to the age of the animal. Seasonality—when the animals died—is estimated using the animals’ characteristics, such as births and shedding of antlers that occur only in certain seasons. Migratory patterns are also useful for determining the time of year when many species of mammals and birds died.

    One last feature that is important to archaeologists is whether the animals were domesticated or wild. As with plants, many physical properties of an animal change as a result of domestication. In general, as they are domesticated, animals tend to get smaller, and changes in their diets can be reflected in their teeth. The presence of some agricultural tools such as plows and yokes indicate that the animals were used to work the land. Finally, some deformities and diseases evident on animal skeletons also point to domestication; osteoarthritis, for example, is often present in the lower limbs of animals used for plowing and transportation.

    Finally, to truly understand what human occupants of a site ate, archaeologists examine and analyze their teeth. Abrasive particles in food can leave striations on the enamel, and the orientation and length of the striations are directly related to the occupants of the site and their food preparation and cooking processes. Abrasive particles in food also lead to tooth decay. Native Californians, for example, routinely ate acorn meal, an extremely gritty food that left marks on their teeth and accelerated tooth decay, distinguishing them from other native people who did not consume acorns. Substantial tooth decay and loss can also be an indicator of diets dominated by starchy and sugary foods and carbohydrates, which would have been consumed because they were the most abundant food source. In recent years, analysis of isotopic markers found in both teeth and human bones have expanded our knowledge of past peoples’ long-term dietary patterns, including whether they relied primarily on land or marine resources for food. Additionally, isotopic markers can identify substantial shifts in diets, which are typically understood to have arisen when individuals moved to new locations.

    Terms You Should Know

    • diet
    • diatoms
    • macrobotanical
    • macrofauna
    • meal
    • meat weight
    • microbotanical
    • microfauna
    • minimum number of individuals (MNI)
    • number of identified specimens (NISP)
    • owl pellets
    • paleoethnobotany
    • palynology
    • phytoliths
    • sedimentology
    • zooarchaeology

    Study Questions

    1. Suppose you have an archaeological site that contains the remains of sloth bones. In the assemblage are 6 phalanges (toe bones), 5 complete skulls, 10 femurs, and 55 vertebrae. Calculate the MNI and NISP for the sloths at this site.
    2. What can phytoliths and diatoms tell archaeologists about a past environment?
    3. What is the difference between a meal and a diet? Give an example.
    4. What specific kinds of archaeological evidence related to flora and fauna can provide archaeologists with clues that the site was occupied by agriculturalists?
    5. Why are macrofauna less useful than microfauna when reconstructing the past environment?