Molluscs (Invertebrates): Analyses in Environmental Archaeology

Introduction

Due to their variable but generally high inorganic content, shells of the phylum Mollusca constitute one of the most durable categories of biogenic finds in the global archaeological record. Mollusc shells are omnipresent and often highly visible in the archaeological contexts across the globe, with the rare exception of wet-preserved contents of acidic bog contexts. The nature and quantity of archaeological mollusc shells vary tremendously among sites, chronological periods, and geographic areas, from 125 ka BP sites associated with early modern humans in eastern Africa (Stinger 2000) to elaborate ornaments from Pre-Columbian Colombia (Carvajal-Contreras 2011). Depending on the geographic area and research question, investigations may focus on molluscs of terrestrial, freshwater, or marine origin, and they may focus on molluscs that were exploited as food resource or as raw material in artifact manufacture. Because mollusc shells archive changes in their ambient environment as they grow incrementally (Richardson 2001), archaeological mollusc shells can become subjects of independent or integrated studies of paleoenvironmental conditions.

Definition

The analysis of mollusc remains from archaeological contexts is an integral part of environmental archaeology and zooarchaeology. Both human-modified and naturally occurring mollusc remains can be subject to molluscan analysis in archaeology. The nature of archaeological mollusc evidence can be alternatively classified in terms of different molluscan taxa and habitats. Archaeological molluscs of terrestrial origin consist of gastropods and are colloquially dubbed as land snails. Molluscs originating from marine environments mainly comprise both gastropods (e.g., whelks, topshells, limpets) and bivalves (e.g., clams, oysters), but remains of other classes of marine molluscs such as cephalopods (typically cuttlefish bones) and scaphopods (typically Dentalium shells) may also occur commonly in certain contexts (Fig. 1). Artifacts made of molluscs, molluscs that represent food, and naturally occurring molluscs are usually handled separately from each other.

Molluscs (Invertebrates): Analyses in Environmental Archaeology, Fig. 1

Examples of mollusc shells that occur frequently in archaeological contexts (1) Scaphopoda, Dentalium shell; (2) Gastropoda, terrestrial (land) snail; (3) Gastropoda, Cypraeidae, “cowrie shell”; (4) Gastropoda, Patella rustica; (5) Cephalopoda, Sepia sp., “cuttlefish bone”; (6) Bivalvia, Chamelea gallina

The study of archaeological mollusc shells is increasingly commonly referred to as “archaeomalacology” since the beginning of the twenty-first century (Bar-Yosef Mayer 2005; Çakırlar 2011). The analysis of mollusc shells tackle a seemingly unlimited range of anthropological and paleoenvironmental issues (Claassen 1998). Analytical methods of archaeomalacology include taxonomic identification, sclerochronology (incremental analysis), taphonomy, biometry, quantitative estimations of abundance, ubiquity, dietary contribution, and habitat construction, as well as experimental archaeology of artifact technology and ethnoarchaeology. Common themes in the study of archaeological molluscs include dietary reconstruction, long-distance contact, artifact technology and use, symbolic uses of shells pertaining to belief systems and representation of socioeconomic class and status, industrial activities, seasonality of food acquisition, and human exploitation pressure on marine ecosystems. Theoretical approaches to archaeomalacology have been largely dominated by optimal foraging concepts on the one hand and culture-historical approaches on the other.

Historical Background

The study of archaeological molluscs has developed as a distinct field within environmental archaeology (Brothwell & Higgs 1969) and zooarchaeology (Grigson & Clutton-Brock 1984). J. Evans’ work on land snails in the context of British archaeology has played a key role in the recognition of mollusc remains as a source of paleoenvironmental information in the UK (Evans 1972). With the rise of Middle-Range Theory in archaeology and New Archaeology, the field developed rapidly in North America, focusing mostly on developing methods to decipher the meaning of gigantic masses of mollusc remains in coastal shell remains for post-Pleistocene adaptations of hunter-gatherer-fisher groups. The historically important study of Ertebølle culture in prehistoric northwestern Europe has also benefited from these international developments in terms of the methodological aspects pertaining to related molluscan evidence.

One landmark in the history of archaeological mollusc analysis is a pilot study that used the light stable isotopic (carbon and oxygen) compositions of archaeological Cerastoderma glaucum (lagoon cockle) incremental biocarbonate in estimating shellfish gathering seasonality (Shackleton 1970). Further methodological advancements in applications of sclerochronology (analysis of ontogenic incremental shell patterning) and shell ecomorphology – relating shell size and shape to molluscan habitats – continue to contribute to the methodological development of the field (Michel et al. 1992).

Key Issues/Current Debates

Studies of archaeological mollusc shells contribute to current debates concerning a number of key issues in archaeology, ranging from the evolution of shared symbolism in recent species of Homo (e.g., D’Errico et al. 2005) to the reconstruction of past human impact on marine resources to serve as a baseline for conservation efforts (Marelli & Arnold 2001).

Some of the most tangible lines of archaeological evidence related to the biological and cognitive evolution of recent Homo sub/species occur in the form of mollusc shells. Perforated Nassarius shells from human encampments dating back to c. 80 thousand years ago constitute some of the earliest ornaments used by humans in Africa (D’Errico et al. 2005). The anthropogenic origin of the perforations was established by experimental work on modern shells. Taphonomic observations using SEM microscopy showed use wear, indicating that perforated objects were strung and probably worn as personal ornaments. Recent well-dated finds indicate that Neanderthals in Europe also manufactured and used perforated and ochre-dyed marine molluscs (Zilhão et al. 2010). The power of such studies in convincing others to see the tangible imprints of hominid symbolism comes from their vigorous use of combined actualistic and stratigraphic research. Experimental work and comparative SEM studies of results have also been of great use in reconstructing the manufacture process and utilization of mollusc shell objects of symbolic value in more recent periods, for example, in aboriginal Australia (Szabó et al. 2007).

Although claims about the significance of the role that marine molluscs played as a food resource during Homo sapiens’ dispersal out of Africa – together with other marine food resources enabling them to explore coastal routes – have sparked some attention (Stinger 2000), for the time being, evidence for intensive exploitation of molluscs by early modern humans can only be substantiated for the later Palaeolithic phases in Southern Africa (Middle Stone Age, c. 50 ka BP) (Klein et al. 2004). Intensive exploitation of marine molluscs, however, does not become evident until the widespread appearance of shell middens during the Late Pleistocene and Early Holocene on almost all coasts of the world, from Japan to Denmark and Peru (Waselkow 1987). Despite the amplitude and ubiquity of mollusc remains at these and subsequently formed shell middens, whether molluscs constituted, in simplest terms, a dietary staple or supplement for coastal groups who occupied them is still debated (Fa 2008).

The various methods developed to assess the dietary role of molluscs for past human groups, as well as other issues pertaining to shell midden archaeology, such as site duration and seasonality, have also been received with mixed criticism and praise. For example, Claassen (1998: 49) has called for caution toward the common use of decrease in mean shell size as a proxy for declining survivorship in mollusc populations due to human exploitation, arguing that the method dismisses other factors – including pressure from predators other than humans – as potential causes for changes in shell size. Similar debates on methodology have gradually led to the advancement of the analytical procedures used to investigate archaeological molluscs, leading to the more common integration of actualistic research on geographically coherent modern mollusc populations as a means of modeling past human behavior relating to shellfish use.

Other lines of actualistic research, such as ethnographic observations of forager groups, have greatly added to our understanding of the formation of mollusc evidence (Meehan 1982). To these, we can add the contribution of experiments conducted by Ruscillo (2005) that shed light on the formation of the mollusc evidence in detecting origins and scale of a dye industry in the Mediterranean region that used the purple substance secreted by Muricid snails’ hypobranchial gland as raw material (Fig. 2). The so-called murex or purple dye industry is mentioned in the Old Testament and by Classical authors. The antiquity and nature of ancient dye manufacture using Muricid snails is a frequently visited issue also in South American archaeology.

Molluscs (Invertebrates): Analyses in Environmental Archaeology, Fig. 2

A sample of crushed Hexaplex trunculus (Muricidae) snails from Late Bronze Age Troy. The shells are crushed in the process of dye manufacture

International Perspectives

Current international research on archaeological molluscs can be summarized into three broad categories: scholarship that focuses on archaeological molluscs as artifacts, molluscs as dietary remains, and molluscs as climatic archives. While artifacts made of molluscs tend to receive more scholarly attention in parts of the world where molluscs played a more visible role in the symbolic world of past cultural groups (e.g., Pre-Columbian Meso-America), in other parts of the world where shell middens are abundant (e.g., Denmark, Japan, California), archaeological molluscs are commonly investigated to test hypotheses relating to the adaptations of hunter-forager groups. Studies that consider the role of molluscs as a food resource in past farmer-herder societies are significantly less common. In studies of post-Neolithic, sedentary societies, mollusc remains (sometimes including fossil molluscs) are commonly used to map long-distance exchange patterns (e.g., Red Sea shells in Bronze Age Mesopotamia), ritual behavior (e.g., mollusc shells adorning the dead), symbolism, and artifact technology. If the variability of the prominence of these two research foci is in part determined by the nature of evidence that varies from one region to the other, it is also in large part dictated by dominant regional academic traditions. Although the exploration of archaeological molluscs, especially land snails, as vessels of past environmental conditions has left a significant impact on the archaeological traditions of some countries like the UK (Evans 1972), this resource has gone almost completely unnoticed in others.

The Archaeomalacology Working Group of the International Council for Archaeozoology (ICAZ) has been fundamentally instrumental in bringing together the multiplicity of international perspectives since its establishment in 2002. Admittedly, proceedings and newsletters of the group (Bar-Yosef Mayer 2005; Çakırlar 2011) testify to its limited success in embracing shell midden and sclerochronological research.

Future Directions

The field of sclerochronology has witnessed a huge leap forward in the recent decade (Schöne & Gillikin 2013), but it unfortunately remains almost entirely unrelated to anthropological (primarily forager behavior) and paleoenvironmental research encapsulated by archaeomalacology. The next decade will hopefully bring along effective communication between archaeomalacology and sclerochronology that will create important opportunities for application in both fields. For the advancement of the analysis of mollusc artifacts, there is ample room toward the under-explored sources of ethnography and use-wear studies. The archaeology of mollusc remains would also benefit from more effective integration with ichthyoarchaeology especially in forming firm baselines for research in conservation biology.

The above-mentioned lines of research, with their differing foci on artifactual mollusc remains, dietary mollusc remains, and mollusc remains as paleoenvironmental proxies, are likely to prevail and progress as largely independent specializations. At the same time, recent studies give clues toward the likelihood that greater shared ground is to be found across the existing “subdisciplines” with interest in archaeological molluscs. This is evident, on the one hand, in the greater emphasis put on the biological and environmental properties of worked and used shells, and in the attention paid to the taphonomy of mollusc remains considered to represent dietary activities on the other, leading to better understandings of, for example, site formation processes. Such developments can only be beneficial for the progress of the field as a whole.

Cross-References

Archaeology and the Emergence of Fields: Environmental

Biometry in Zooarchaeology

Blombos Cave: The Middle Stone Age Levels

Ethnoarchaeology

Experimental Maritime Archaeology

Human Impacts on Ancient Marine Ecosystems

International Council for Archaeozoology (ICAZ)

Middle-Range Theory in Archaeology

Molluscs (Isotopes): Analyses in Environmental Archaeology

New Archaeology, Development of

Taphonomy: Definition

Zooarchaeology