Archaeological Shell Research Articles

Red abalone collecting and marine water temperature during the Middle Holocene occupation of Santa Cruz Island, California

Oxygen isotope values derived from prehistoric mussel (Mytilus californianus) shell calcite are used to determine whether sea-surface temperatures in the vicinity of the Punta Arena site (CA-SCRI-109) on Santa Cruz Island, California, were cooler than present between 6300 and 5300 cal BP. This site and others in the western sector of the island dating to this period are distinctive because of the presence of large red abalone (Haliotis rufescens) shells, a species that historically has been subtidal around Santa Cruz and the other northern Channel Islands. Comparison of temperature values derived from archaeological shells with those from modern mussel shells, along with water temperatures derived from satellites, indicates that waters were cooler during the 6300 to 5300 cal BP period. These results are consistent with a previous study and support the interpretation that collection of red abalone during the 6300–5300 cal BP period was partly the result of cooler water temperatures that made this large mollusk more available to foragers in the intertidal or shallow subtidal zone.

14C Marine Reservoir Variability in Herbivores and Deposit-Feeding Gastropods from an Open Coastline, Papua New Guinea

Herbivorous and deposit-feeding gastropods are a major component of archaeological shell middens worldwide. They provide a wealth of information about subsistence, economy, environment, and climate, but are generally considered to be less than ideal for radiocarbon dating because they can ingest sediment while they graze, inadvertently consuming terrestrial carbon in the process. However, few studies of 14C activity in herbivores or deposit-feeding gastropods have been conducted into this diverse range of animals that inhabit many environmental niches. Here, we present results investigating 14C variability in shells belonging to the families Strombidae and Potamididae from the Bogi 1 archaeological site, Caution Bay, southern coastal Papua New Guinea (PNG). These shells make up 39.3% of the shell MNI in the excavation units studied and some of these species are the most common taxa of neighboring sites. It would therefore be advantageous to establish if there are any 14C offsets associated with such animals, and identify those that can give reliable calendar ages. Our methodology combines a high-resolution excavation protocol, selection of short-lived samples identified to species level, and a triisotope approach using 14C, δ13C, and δ18O to evaluate the source of variability in shells. Our results indicate that considerable variation exists between different species of Strombidae with some inhabiting muddier environments that act as sinks for limestone-derived sediments with depleted 14C content. The magnitude of variation is, however, overshadowed by that measured in the mudwhelk, Cerithidea largillierti, which has the largest spread in 14C of any shellfish studied so far at Caution Bay. This animal ingests sediment within the estuary that contains 14C derived from both enriched and depleted sources.

Quantifying shell weight loss in archaeological deposits

ABSTRACT While a range of physical and chemical taphonomic processes are known to affect archaeological shell assemblages, it has been difficult to directly quantify the effects of these degradational processes on the shell itself. Here the measurements of Anadara granosa shell features are used to derive morphometric equations for estimating expected shell weights. A cubic regression model is developed to this end, based on measurements of all shell elements of complete A. granosa valves, resulting in high predictive power. The morphometric method proposed here therefore allows for the comparison of observed and expected shell weights to determine the extent of weight loss as an indication of these processes. A case study is presented by applying these morphometric equations to a midden assemblage from northeast Arnhem Land to investigate potential bias in shell preservation. This study demonstrates the efficacy of the proposed method, and the need to assess the interaction of different taphonomic processes on a site and species‐specific basis.

Morphometric analyses of Batissa violacea shells from Emo (OAC), Gulf Province, Papua New Guinea

ABSTRACT Archaeological investigations of human predation pressures on shellfish usually rely on measurements of complete shell specimens. However, most archaeological shell assemblages consist predominantly of broken shells, limiting measurable sample sizes, and thus potentially biasing results in cases where shell fragmentation is biased towards particular size classes (due to shell size‐fragility correspondences). This paper presents a recent application of morphometric analyses on the Batissa violacea assemblage from Emo, an early ceramic site from the Gulf Province, Papua New Guinea. Our method enabled most shell valves, fragmented or not, to be accurately and comparably measured for size. The results reveal a close match between the commencement of occupation and maximum shell sizes in a sequence of occupational phases, each separated by many decades to hundreds of years of site abandonment. While each occupational phase begins with peak mean shell sizes, the later peaks never again attain the mean shell size of the initial phase. As each phase progresses, shell sizes diminish until abandonment, and then the same pattern starts again with the next phase. Identical trends were obtained from two separate excavation squares. We interpret these results to indicate that while people may have abandoned the site of Emo between the occupational phases, they did not abandon the region, continuing to exploit local shellfish beds, albeit less frequently than during the site's occupation. These results highlight the ability of local (site‐specific) archaeological shell data to shed light on regional demographic and occupational trends.

Integrated Archaeozoological Research of Shell Middens: New Insights Into Hunter-Gatherer-Fisher Coastal Exploitation in Tierra Del Fuego

ABSTRACT Shells of Nacella magellanica are abundant in archaeological shell middens distributed along the Beagle Channel. In this study we analyzed the oxygen isotopic composition of shells of this species to obtain information on its seasonal exploitation patterns by hunter-gatherer-fisher groups in this region during the nineteenth century. Oxygen isotopic data from shells recovered from Lanashuaia and from some occupations of Túnel VII (both contact sites) indicate that N. magellanica was gathered in different seasons. Our data agree with fauna-derived seasonal reconstructions, and collectively these data provide more detailed economic scenarios. Comprehensive results confirm that in the nineteenth century, Yamana people continuously occupied the coast of the Beagle Channel by means of short-lived campsites.

Isotopic evidence for climate change during the Vandal Minimum from Ariopsis felis otoliths and Mercenaria campechiensis shells, southwest Florida, USA

Archaeological evidence from coastal southwest Florida suggests this region and its local inhabitants (the Calusa) were affected by drought and cooling during the Vandal Minimum climate episode (ad 500–800). To test this hypothesis, we reconstructed seasonal-scale climate conditions using stable oxygen and carbon isotope ratios (δ18O and δ13C) preserved in Ariopsis felis otoliths and Mercenaria campechiensis shells. Comparing δ18O records from both species distinguishes between cool versus warm and wet versus dry conditions. δ18O values from four otoliths indicate cooling of winter temperatures occurred in the early Vandal Minimum (ad 500–600) and late half of the middle Vandal Minimum (ad 650–700). Persistent dry summers punctuated by occasional years with wet summers throughout the Vandal Minimum were detected from δ18O values of eight archaeological shells. Our climate reconstructions are in good agreement with archaeological observations and with the cool and dry conditions documented in Europe.

Developing baseline data to understand environmental change: a geochemical study of archaeological otoliths from the Coorong, South Australia

Otoliths are calcium carbonate structures found in the inner ear of teleost fish. While they are routinely studied by marine scientists, analyses of otoliths recovered from archaeological sites in Australia and the Pacific have generally been restricted to identification of species and sometimes the fish age. Otoliths can also provide information on the season of catch, and, through trace element analysis, allow the reconstruction of environmental conditions experienced by fish. In this study, we use otoliths from mid- to late Holocene aged archaeological shell middens at the Coorong (South Australia) to examine species present, season of catch, age of fish and environmental conditions experienced by fish. Results demonstrate that the majority of the fish (identified as Argyrosomus japonicus and Acanthopagrus butcheri) were caught in freshwater environments during the warm season, and had grown to an age and size indicative of their having reached sexual maturity. This study provides data indicating fluctuating levels of salinity in the estuary, which are significantly lower than the hypersaline conditions experienced today. Ultimately, this project highlights the usefulness of conducting more detailed investigations of otoliths, including geochemical analyses, to address a wide range of research questions in archaeology and palaeoenvironmental research.

Micromorphological perspectives on the stratigraphical excavation of shell middens: a first approximation from the ethnohistorical site Tunel VII, Tierra del Fuego (Argentina)

Due to their problematic stratigraphy, shell middens have traditionally been excavated by artificial stratigraphical cuts. This approach has often led to the obliteration of the original depositional sequence, removing important information regarding depositional and post-depositional processes, and human frequentation. Since the 1970s, an Argentinian team has been excavating archaeological shell middens in the Beagle Channel with a detailed stratigraphical approach, based on the excavation of actual depositional units (peeling), rather than artificial cuts. In the 1980s, Spanish archaeologists joined the Argentinean team and launched a series of new projects involving the excavation of ethnohistorical Yamana fisher-hunter-gatherer sites. The first excavated midden site was Tunel VII, from which two monolith columns of about 50 cm each (C11 and C12) that spanned the whole stratigraphy were extracted. The two columns were consolidated with resin, and two series of thin sections produced to corroborate stratigraphical observations made in the field, and to verify hypotheses related to the formation of archaeological shell midden sites. We present here the first results obtained from the microscopical observation of seven thin sections from column 11 (West column), extracted from a portion of the profile originally described as corresponding to the hut entrance and associated floor. The observation of microscopical features invisible in the field has provided supplemental information about the depositional and post-depositional processes affecting shell midden sites. We have also preliminarily defined a number of micromorphological characteristics identifying human activities such as discrete shell deposition events, phases of preparation of the hut floor, and compression by repeated trampling. Finally, we have explored the possibility of establishing some guidelines to characterise the length and character of frequentation phases of the site previous to its final abandonment at the beginning of the 20th century.

A New Radiocarbon Pretreatment Method for Molluscan Shell Using Density Fractionation of Carbonates in Bromoform

Coastal archaeological sites that lack organic remains for radiocarbon dating are often abundant sources of molluscan shells. As a substitute for materials such as bone and charcoal, shells can be analyzed with14C dating to determine a site's age. Despite their being convenient, non-mobile archaeological artifacts, molluscan shells are plagued by several issues, including carbonate remodeling, in which aragonite in shells is converted to calcite as predicted by thermodynamics. We present here a carbonate density separation technique that addresses the issue of carbonate remodeling. Using a density fractionation with bromoform, aragonite concentrations are enriched in shells that have undergone significant remodeling. The technique has been applied to archaeological shells and has returned dates that are younger than those previously determined for the same shells.

An expanded radiocarbon age calibration procedure to correct for the marine reservoir effect in mixed marine and terrestrial samples

Recently, the importance of statistical and probabilistic analysis to derive accurate 14 C data has been recognized. This paper discusses a 14 C calibration procedure to correct marine reservoir effect using the marine source contribution estimated as a probability distribution. In addition, we also developed the marine source estimation with δ 13 C and δ 15 N for the 14 C calibration in order to cover a complex mixture of terrestrial and marine carbon such as a human. In our calibration procedure, the 14 C date is weighted with the probability distribution of marine source contribution and the calibrated date depended on the marine 14 C intake can be evaluated. The age range calibrated by our procedure can be also reduced more than by conventional calibration methods. We illustrated the character of our calibration procedure by the example of human bones found from the archaeological shell mounds in Japan.

High-resolution sclerochronological analysis of the bivalve mollusk Saxidomus gigantea from Alaska and British Columbia: techniques for revealing environmental archives and archaeological seasonality

The butter clam, Saxidomus gigantea, is one of the most commonly recovered bivalves from archaeological shell middens on the Pacific Coast of North America. This study presents the results of the sclerochronology of modern specimens of S. gigantea, collected monthly from Pender Island (British Columbia), and additional modern specimens from the Dundas Islands (BC) and Mink and Little Takli Islands (Alaska). The methods presented can be used as a template to interpret local environmental conditions and increase the precision of seasonality estimates in shellfish using sclerochronology and oxygen isotope analysis. This method can also identify, with a high degree of accuracy, the date of shell collection to the nearest fortnightly cycle, the time of day the shell was collected and the approximate tidal elevation (i.e., approx. water depth and distance from the shoreline) from which the shell was collected. Life-history traits of S. gigantea were analyzed to understand the timing of growth line formation, the duration of the growing season, the growth rate, and the reliability of annual increments. We also examine the influence of the tidal regime and freshwater mixing in estuarine locations and how these variables can affect both incremental structures and oxygen isotope values. The results of the sclerochronological analysis show that there is a latitudinal trend in shell growth that needs to be considered when using shells for seasonality studies. Oxygen isotope analysis reveals clear annual cycles with the most positive values corresponding to the annual winter growth lines, and the most negative values corresponding to high temperatures during the summer. Intra-annual increment widths demonstrate clear seasonal oscillations with broadest increments in summer and very narrow increments or no growth during the winter months. This study provides new insights into the biology, geochemistry and seasonal growth of S. gigantea, which are crucial for paleoclimate reconstructions and interpreting seasonality patterns of past human collection.

Beyond means to meaning: using distributions of shell shapes to reconstruct past collecting strategies

Archaeological shell assemblages are often compared by the average size of a given shell species, with smaller average sizes taken as indicating greater human exploitation. This is simplistic, since the average size of a species of shellfish naturally varies considerably across a shore and over time. This distribution of shell size, shape and density varies systematically, according to a predictable pattern. Ancient shellfish collecting strategies can be reconstructed by comparing distributions of size, shape and age of archaeological shells to this systematic pattern. Methods for recovering these distributions from archaeological shell assemblages are outlined, and some recent applications to archaeological shell assemblages are highlighted.

Isotope sclerochronology of Mercenaria mercenaria, M. Campechiensis, and their natural hybrid form: Does genotype matter?

Abstract Isotopic variation in northern and southern hard clam (quahog) shells is used in studies including paleoecology, paleoclimatology, and archaeology. It is unknown, however, whether species-specific isotopic differences exist. Three genotypes—Mercenaria mercenaria, M. campechiensis, and their natural hybrid form—are found in coastal Florida waters and differentiation of genotypes can be difficult to determine morphologically. This issue may be problematic when using archaeological shells as paleoclimate archives, because genetic analysis cannot be done on such specimens. Their co-occurrence in coastal Florida waters provides a unique opportunity to study whether all three genotypes of modern individuals record the same environmental information preserved as variation in oxygen and stable carbon isotope ratios. A random sample of 49 individuals collected alive at the same time and from the same locality in Pine Island Sound were classified to genotype using allozyme electrophoresis. Three juveniles ...

Estimating age by tooth wear of prehistoric human remains in Brazilian archaeological sites

AbstractThe occlusal surfaces of 298 permanent maxillary and mandibular molar teeth of prehistoric shellfish‐gatherer subjects from the Piaçaguera and Tenorio sites (4930 to 1875 BP), near the central‐northern coastline of São Paulo, Brazil, were examined for classification of macro‐wear stages. Molar tooth wear is an indication of masticatory activity and can be used in the estimation of age at death. The examination of visual and schematic aspects of occlusal macro‐wear used a visual chart proposed by Brothwell, which includes the three superior and inferior, left and right, permanent molars. Three examiners performed the macroscopic observations twice under the same conditions. The resulting age estimates were compared with previous information of age estimated by skeletal examination. A reduced intra‐ and inter‐observer variation was observed; all re‐examinations indicated discrepancies of less than two years for the upper and lower limit of the age range estimates. The procedure was also considered consistent with the skeletal method used for age estimation of human remains excavated in Brazilian archaeological shell mounds, with a discrepancy of less than 8.22 years between the upper and lower limits of estimates by both methods. Age classification by the occlusal molar wear may be a useful tool for the classification of archaeological findings, mainly when only fragmentary skeletal remains are excavated. The current results indicate that the application of the Brothwell chart for Brazilian archaeological series presented satisfactory results of consistency, and its expanded use may represent a relevant adjunct for research. Copyright © 2006 John Wiley & Sons, Ltd.

Geochemical variation in microstructural shell layers of the southern quahog ( Mercenaria campechiensis): Implications for reconstructing seasonality

Shells of the northern and southern quahogs ( Mercenaria mercenaria and Mercenaria campechiensis, respectively) from paleontological and archaeological deposits have been used to reconstruct climate, environmental conditions, and ecological relationships. Seasonal fluctuations in temperature and salinity are recorded in shell carbonate as variations in δ 18O and δ 13C values and Sr : Ca ratios; however, these environmental proxies have not yet been calibrated for M. campechiensis. Previous geochemical studies of quahog shells focused on the outer prismatic layer as an ecological archive. The outer layer is often not preserved in fossil and archaeological shells. Moreover, recent innovations in microsampling techniques allow high-resolution sampling of the middle cross-lamellar layer. This study tests whether outer prismatic and middle cross-lamellar layers record similar variations in δ 18O and δ 13C values and Sr : Ca ratios in modern shells of M. campechiensis and whether profiles are similar among individuals. The last 2 years of shell growth from three individuals (6, 7, and 9 years old) collected alive near Bokeelia, southwest Florida, were microsampled for geochemical analyses. δ 18O varies seasonally relative to translucent (summer) and opaque (winter) growth increments. Variation of δ 18O from outer and middle layers are identical within and among shells; however, the oldest individual did not preserve the most positive values represented in the two younger shells. δ 13C from both layers are similar within shells, although the outer layer is more variable and the range of values varies somewhat among individuals. Sr : Ca ratios from the outer and middle layers within shells do not track each other well, and profiles among individuals are different. To evaluate whether a seasonal signal was present, Sr : Ca ratios were compared to δ 18O values. There was no co-variation within the outer layer in any of the shells; therefore, this layer should be avoided when using Sr : Ca ratios as a temperature proxy. The middle layer from the 6-year-old shell showed no co-variation, the 7-year-old shell exhibited a moderate negative co-variation ( r 2 = 0.55, p < 0.01), and the 9-year-old shell reflected a strong negative co-variation ( r 2 = 0.72, p < 0.01). These findings suggest that Sr : Ca ratios from the middle layer may serve as a proxy for temperature only in older individuals with slower growth rates. Either shell layer can be sampled for assessing seasonality using δ 18O, and environmental interpretations made using δ 13C values should be treated with caution.

Stable isotopes and sclerochronology of the bivalve Mesodesma donacium: Potential application to Peruvian paleoceanographic reconstructions

Reconstructing the past ENSO (El Niño Southern Oscillation) interannual variability requires very high resolution sea surface temperature (SST) proxies. In order to compensate for the lack of coral archive in the Eastern Pacific cold tongue, we studied the potentiality of the bivalve species Mesodesma donacium as a SST tracer for the Peruvian coast. Biomineralisation cycles and growth line formation in the shells are shown to be controlled by tides. The sclerochronology based on fortnightly cycles allowed us to compare local SST data with high resolution shell records. As a result of the high correlation between SST and aragonite δ 18O, we calculated a linear SST–fractionation relationship for the 14–20 °C range: T ( ° C ) = ( 17.41 ± 1.15 ) − ( 3.66 ± 0.16 ) ∗ ( δ 18 O arag./PDB − δ 18 O wat./SMOW ) . The difference from the commonly used Grossman and Ku (1986) [Grossman, E.L., Ku, T.L., 1986. Oxygen and carbon fractionation in biogenic aragonite: temperature effect. Chemical Geology 59, 59–74] equation suggests the potential existence of a species dependence of vital effect within bivalves. This preliminary equation allows monthly-scale SST reconstructions with a ± 1.5 °C precision using M. donacium archaeological shells from southern Peru, giving potential insights into the problem of past ENSO behaviour.

Oxygen isotopic evidence for greater seasonality in Holocene shells of Donax variabilis from Florida

Donax variabilis, the variable coquina clam, has been a common inhabitant of exposed sandy beach intertidal and shallow subtidal zones in the southeastern United States throughout the Pleistocene and Holocene. It is ideally suited for paleotemperature studies because it is restricted to environments of well-mixed, normal-marine seawater with a fairly uniform isotopic composition. As a result, oxygen isotopic variability in D. variabilis shells is largely explained by temperature variation. Although D. variabilis is small and short-lived, its shell represents an important paleoclimate archive because of its unique habitat preference. High-resolution sampling of individual D. variabilis shells and comparison of oxygen isotopic temperature profiles with historical seawater temperatures from the northeastern Florida coast indicate rapid shell growth over a brief life span of three to five or six months. Analysis of two modern shells reveals a close correspondence between isotopically determined water temperatures and historical water temperatures during the spring–summer growing season. Paleotemperature profiles from four archaeological shells, however, suggest a longer growth interval spanning summer–autumn. Two Preceramic Archaic Period shells (ca. 4240 and 5570 14C yr BP) and two Orange Period Archaic shells (ca. 3600 and 3760 14C yr BP), from four different archaeological sites, yield paleotemperatures that average 3.5 °C higher than present summer–autumn water temperatures. These warm paleotemperatures highlight seasonality differences associated with the mid-Holocene Hypsithermal climatic interval in this region.

Morphometric analysis of limpets from an Iron-Age shell midden found in northwest Portugal

The present work reports an analysis of a shell midden found in Terroso hillfort, an important Iron-Age oppidum located in northwest Portugal. The midden was dated from the latest phase of occupation of the hillfort, between the Ist century BC and the Ist century AD (Roman period), and contained 684 well-preserved Patella shells. The identification of archaeological shells was carried out comparing them with modern specimens collected in two shores in the neighborhood of the hillfort. The identification of modern shells was based on radula pluricuspid teeth and shell morphology. Relative abundance of Patella species in the Terroso midden was different from modern populations. Archaeological shells were dominated by Patella vulgata, but Patella intermedia was the most abundant species in modern populations. Dimensions of archaeological shells were very different from modern populations. Shell length range and variability in archaeological shells were lower than in the modern populations. Log height vs. length plots for archaeological shells were different from modern populations. Patella shells from Terroso midden was significantly taller then modern specimens. These differences between archaeological shells and modern populations could be due to environmental changes, namely an increase in wave action and intensity. These harsher costal conditions could have resulted from an alteration in the morphology of the coast, caused by a rise in the mean sea level from 2000 years BP to the present. Alternatively or additionally, the observed differences can be related to gathering strategies. Archaeological shells could have been selected by size, and collected preferentially at high shore and in sheltered sites.

Prehistoric and World War II Use of Shell Mounds in Darwin Harbour

Darwin Harbour is one of the largest bays along the Northern Territory coastline. Some shell mounds around the Harbour are renowned as the creations of the scrub-fowl Megapodius reinvardt (Stone 1989). However, the abundant archaeological middens that exist within the region have received little attention. While this failure to explore the archaeology of Darwin Harbour is being remedied in the regional study by Bums (1999), there is still a need for specific studies of site patteming within the region. In particular investigations of chronological and morphological variation in anthropogenic shell deposits and their environmental contexts will assist the evaluation of land-use models. Shell structures in Darwin Harbour exist within a geomorphic context underrepresented in studies of archaeological mounds in the Top End. Shell mounds studied elsewhere in northern Australia by archaeologists are generally on near-flat depositional surfaces produced by coastal progradation and composed entirely of alluvium or coastal sediments, and the interpretation of these sites is tied to the growth of coastal plains (eg. Bailey 1975 ; Baker 1981; Beaton 1985; Woodroffe et al. 1988). In contrast, Darwin Harbour consists of a flooded valley that has had relatively little sediment infilling, leaving a coastline that consists of bedrock and steep colluvial slopes that terminate below the high tide limit. Middens in Darwin Harbour, located on these steep rocky surfaces, are subject to different geomorphic conditions and reflect an environmental history different from mounds in regions such as Kakadu or Princess Charlotte Bay. Â In this paper we describe deposits of shell identified in one portion of Darwin Harbour, and document not only mound structures but also rings of shell. Our purpose is to provide an initial account of the diversity and chronology of these two kinds of archaeological shell deposits around Darwin Harbour and to discuss prehistoric settlement systems in that area of northern Australia. Our investigations focus on Haycock Reach, a small portion of the Harbour coastline which demonstrates a rich archaeological record. Â

Oxygen Isotopic Analysis of Archaeological Shells to Detect Seasonal Use of Wetlands on the Southern Pacific Coast of Mexico

Oxygen isotopic ratios in modern and archaeological marsh clam shells ( Polymesoda radiata) from the Acapetahua Estuary in southwestern Mexico record large scale salinity fluctuations caused by alternating wet and dry seasons. Thus, prehistoric patterns of rainfall can be reconstructed and the season of molluscan death can be estimated. Changes in the oxygen isotopic patterns preserved in marsh clam shells from late Archaic period ( c. 3000–1800 bc) archaeological deposits indicate that the season of shellfish harvesting changed dynamically through time in this region. Based on this study, and other lines of archaeological evidence, we argue that hunter–gatherers during the early stages of the late Archaic period visited locations in the littoral zone throughout the year with a focus during dry season months. Through the late Archaic period a general trend occurred toward wet season use of these locations. This culminated at the end of the late Archaic period with the exclusive use of the littoral zone during wet season months. These data indicate a fundamental shift in the way these estuarine locations were being used. We argue that people living in this region altered their overall subsistence strategy during the late Archaic period due to scheduling conflicts that occurred with the adoption of maize agriculture.