Tracking changes in bone fracture morphology over time: environment, taphonomy, and the archaeological record

Zooarchaeologists have often employed studies of bone fracture morphology as a means of understanding past human cultural activity, and various methodological approaches have been developed for analyzing archaeological broken bone assemblages. It is widely understood that bones degrade over time, however, few studies have attempted to define and quantify the rate at which bones degrade and fracture morphologies change. This study examines degradation in frozen bones (−20 °C) and bones exposed to hot (40 °C) dry conditions. These two simulated environmental conditions represent extreme real-world climates, and allow for an actualistic understanding of the rates of degradation that bones experience in nature. When frozen, bones degrade slowly but significantly, and demonstrate measurable differences in samples frozen for 1, 10, 20, 40, and 60 weeks. In hot, dry conditions, bones degrade very quickly, and demonstrate measurable differences after 1, 3, 7, 14, and 21 days. These data allow for a more detailed understanding of the relationship between the cultural and natural processes that result in bone fracture, and the time period during which bones can be expected to maintain fresh fracture characteristics. This research also has implications for understanding human subsistence and survival strategies and for interpreting the archaeological record.     

Experimental chemical degradation compared to natural diagenetic alteration of collagen: implications for collagen quality indicators for stable isotope analysis

Stable isotopic ratios from archaeological bone collagen are valid palaeodietary indicators, but depend on sufficiently well preserved molecules and several collagen quality criteria have to be fulfilled (mostly collagen wt%, C%; N%, C/N molar ratio). For a reassessment of these quality criteria, and a better understanding of the chemical degradation of bone collagen, experimentally degraded modern bones and 54 archaeological human bones were investigated. In the course of the experimental degradation, alterations of isotopic ratios were paralleled by altered collagen quality criteria. The contrary was found in the case of the archaeological specimens. This implies that the commonly used collagen quality criteria may be insufficient and do not guarantee that stable isotopic values of the gelatine extracts will still represent the original biological signal.     

The Future Preservation of a Permanently Frozen Kitchen Midden in Western Greenland

Abstract

Archaeological materials may be extraordinarily well preserved in Arctic areas, where permanently frozen conditions in the ground slow down the decay of materials such as wood, bone, ?esh, hair, and DNA. However, the mean annual air temperature in the Arctic is expected to increase by between 2·5 to 7·5°C by the end of the twenty-?rst century. This may have a signi?cant warming effect on the soil and could lead to permafrost thaw and degradation of currently frozen archaeological remains. Here we present a four-year monitoring and research project taking place at Qajaa in the Disko Bay area in West Greenland. Qajaa is a large kitchen midden, containing frozen remains from 4000 years of inhabitation, from when the ?rst Palaeo-Eskimos entered Greenland, until the site was abandoned in the eighteenth century. The purpose of the project is to investigate current preservation conditions through ?eld and laboratory measurements and to evaluate possible threats to the future preservation.

Preliminary results show that the archaeological material at Qajaa is still very well preserved, but some microbial decay is observed in the exposed wooden artefacts that thaw every summer. Maximum temperatures are above 0°C in the upper 40–50 cm of the midden and between 0 and ?2°C down to 3 m depth. Thereby the permafrost may be vulnerable to quite small increases in air temperatures. Laboratory measurements show that the decay of the archaeological wood in the midden is temperature-dependent, with rates increasing 11–12% every time the soil temperature increases 1°C. Moreover, the soil organic material produces heat when decomposed, which could have an additional warming effect on the midden. At the moment the water or ice content within the midden is high, limiting the subsurface oxygen availability. Threats to the future preservation are related to further thawing followed by drainage, increased oxygen availability, microbial decay of the organic material, and heat production.     

In situ Preservation Solutions for Deposited Iron Age Human Bones in Alken Enge,Denmark

The rich mass deposition of Iron Age human bone material from the Danish site, Alken Enge, is extraordinary not only from an archaeological perspective but also from a preservation point of view. The main find is situated in a waterlogged, anoxic environment which provides excellent preservation conditions and therefore enables in situ preservation of the human bones. However, major differences in local environmental conditions challenge an in situ preservation of the entire site area as parts of the bone material presently deteriorate. In this paper, a multi-proxy environmental monitoring approach is used to document threats and to suggest the best preservation solution for the archaeological finds, whether in or ex situ.     

Actualistic research into dynamic impact and its implications for understanding differential bone fragmentation and survivorship

The relationship between bone mineral density and archaeological bone survivorship has played a critical role in zooarchaeological and taphonomic studies in recent decades. Numerous studies have suggested that higher-density skeletal element portions survive more frequently than lower-density element portions when archaeological assemblages are affected by some taphonomic processes. Interpretations of density mediated destruction have become commonplace in the archaeological literature, and are often used to explain the absence of certain bone elements and element parts in zooarchaeological assemblages. This study explores the effects of rockfall on bovid elements in varied environmental conditions and the differential survivorship of their element parts, and has implications for understanding the taphonomic processes through which bones are subjected to dynamic loading. Actualistic rockfall experiments conducted on twelve samples of frozen, fresh, and semi-dried bovid bones reveal that the generally low-density epiphyseal ends of bone elements resist fracture and analytical deletion with more frequency than the higher-density diaphyses. This evidence suggests that bone density does not correlate with likelihood of breakage or effective archaeological “destruction” when rockfall and other processes that result in dynamic impact are in action. While this research does not question the relationship between bone mineral density and the likelihood for archaeological survivorship as the result of some taphonomic processes, it presents one specific set of taphonomic processes that result in the differential survivorship of low density bone elements parts and the fragmentation and destruction of higher density element parts. This research presents evidence that shows that dynamic impact is a process capable of fragmenting and sometimes destroying high-density elements while low-density elements survive.     

Degradation of Archaeological Wood Under Freezing and Thawing Conditions—Effects of Permafrost and Climate Change

The degradation of archaeological wood at freezing and thawing temperatures is studied at the site of Qajaa in West Greenland through a combination of environmental monitoring, measurement of oxygen consumption and microscopy of wood samples. Permanently frozen wood is still very well preserved after 2–4000 years, while wood samples that thaw every summer show attack by soft rot and an average density loss of 0.1 g cm^–3 (corresponding to 25% of the dry mass) over the past 27 years. Future increases in temperature may increase the decay rate significantly (Q₁₀ = 4.2 at 0–10°C) but the effects on site depend on local hydrology.     

Avian Remains from Late Pre-colonial Amerindian sites on Islands of the Venezuelan Caribbean

ABSTRACT

This paper presents the results of the analyses of 3793 bird remains archaeologically recovered from seven late pre-Hispanic sites (～AD 1000–1500) on islands of the Venezuelan Caribbean. In order to address subsistence and manufacturing uses of bird bones, we first discuss the recovery process of this unique sample. We proceed to investigate the bones' archaeological contexts as well as the taphonomy in play and analyze diverse bone categories. We found that indigenous peoples consistently targeted several families of birds for food or feathers or both, and that avian bones were used for fashioning tools and adornments. We also discuss possible signatures of island campsite seasonal occupancy as inferred from the bio-ecology of the identified bird taxa. The data suggest that the differentiation of nesting grounds between the Red-footed and Brown Booby in the Southeastern Caribbean may be a result of anthropogenically-induced adaptation. The findings discussed in this paper open challenging avenues for assessing long-term changes in bird communities including the dynamics of resident and wintering bird populations.     

Understanding the variability in freshwater radiocarbon reservoir offsets: a cautionary tale

Freshwater resources in past diets can lead to inaccuracies when attempts are made to ascertain their radiocarbon ages or those of the consumers. Radiocarbon reservoir effects may lead to significant age offsets when the bones or other tissues of these consumers are radiocarbon dated. A number of recent studies have investigated freshwater reservoir offsets. However no study thus far has satisfactorily obtained a ubiquitous freshwater reservoir correction due to variability in the ecosystems analysed. This study tests the possibility of predicting freshwater reservoir effects from the carbonate alkalinity of the water with measurements on modern fish bone and water samples. A predictive capability would be especially valuable in the absence of well-preserved archaeological fish bone. We surveyed samples from lakes and rivers in varying geological settings in Britain and Ireland. Modern fish bone and water samples were analysed to investigate modern radiocarbon offsets from the atmosphere. Archaeological fish bone was also analysed to examine past reservoir offsets at selected sites. Stable carbon and nitrogen isotope values were measured to aid in interpretation of any variability in the offsets. Large freshwater reservoir offsets were measured in some modern and archaeological samples (maximum offset = 1638 ¹⁴C years). The freshwater reservoir offsets in the fish bone were highly correlated with alkalinity of water in modern lake sites analysed. However, a high amount of variation within and between fish species was also evident in the results, precluding the possibility of providing regional corrections for freshwater reservoir offsets from alkalinity although this still may provide a general guideline. The variability is thought to be due to differences in the diet of individual fish.     

The bioerosion of bird bones

This study presents a synthesis of the evidence for modern archaeological, and palaeontological bioerosion of vertebrate tissue. It describes the first evidence for the bioerosion of modern, archaeological and fossil bird bones. A new form of bone bioerosion, known as Hackett tunnels, is defined. The bioerosion of vertebrate tissue by cyanobacteria and algae in modern marine and lacustrine environments is also described. Archaeological evidence indicates that the destruction of bone by bioerosion occurs in other terrestrial environments, such as cave deposits and middens. Bone from marine and lacustrine environments that appears to be macroscopically well preserved can have large amounts of microscopic fabric destruction. © 1997 John Wiley & Sons, Ltd.     

Implications of heat-induced changes in bone on the interpretation of funerary behaviour and practice

Bones submitted to heat experience structural and chromatic modifications. In particular, heat-induced bone warping and thumbnail fractures have been linked to the burning of fleshed and green bones – where the soft tissues have been removed from the bones soon after death – in contrast to dry bones. Those have been suggested as indicators of the state of the individual before being burned thus allowing inferences about the funerary behaviour of archaeological populations. A large sample of 61 skeletons submitted to cremation has been examined for the presence of both of these heat-induced features. Although uncommon, bone warping and thumbnail fractures were present in some of the skeletons demonstrating that its presence is not restricted to the burning of non-dried bones as generally believed. Rather than being an indicator of the presence of bones with soft tissues, bone warping seems to be more of an indicator of the preservation of collagen–apatite links which can be maintained on dry bones with low collagen deterioration. In addition, our results also do not confirm thumbnail fractures as an exclusive sign of the burning of bones with soft tissues. As a result, these heat-induced changes should be used with caution when trying to infer about the pre-burning state of an individual.     

Sub‐micron spongiform porosity is the major ultra‐structural alteration occurring in archaeological bone

Total pore volume and pore size distribution are indicators of the degree of post‐mortem modification of bone. Direct measurements of pore size distribution in archaeological bones using mercury intrusion porosimetry (HgIP) and back scattered scanning electron microscopy (BSE‐SEM) reveal a common pattern in the changes seen in degraded bone as compared to modern samples. The estimates of pore size distribution from HgIP and direct measurement from the BSE‐SEM images show remarkable correspondence. The coupling of these two independent approaches has allowed the diagenetic porosity changes in human archaeological bone in the >0.01 µm range to be directly imaged, and their relationship to pre‐existing physiological pores to be explored. The increase in porosity in the archaeological bones is restricted to two discrete pore ranges. The smaller of these two ranges (0.007–0.1 µm) lies in the range of the collagen fibril (0.1 µm diameter) and is presumably formed by the loss of collagen, whereas the larger pore size distribution is evidence of direct microbial alteration of the bone. HgIP has great potential for the characterization of microbial and chemical alteration of bone. Copyright © 2002 John Wiley & Sons, Ltd.     

Biological mineral content in Iberian skeletal cremains for control of diagenetic factors employing multivariate statistics

The aim of this study was to define a strategy for a correct selection of bone samples by employing inductively coupled plasma optical emission spectroscopy (ICP-OES) for reconstructing the biological mineral content in bones through the determination of major elements, trace elements and Rare Earth Elements (REE, lanthanides) in skeletal cremains of ancient Iberians (III–II B.C), discovered in the Necropolis of Corral de Saus (Moixent, Valencia) between 1972 and 1979. The biological mineral content was determined taking into account diagenetic factors. A control method for a better reading of results was applied. To explore large geochemical datasets and to reduce the number of variables, Principal Component Analysis (PCA) was used, thus, providing a deeper insight into the structure of the variance of the dataset. PCA shows that the elemental profiles of bone and soil samples are clearly different. Bone samples obtained from the outer bone layer were shown to have a different elemental composition; more similar to soil samples than samples of the inner bone layer. PCA scores and loadings plots were preferred to dendrograms obtained using Cluster Analysis, due to the limits of the latter one to appreciate the spatial ordering of samples. Partial least squares discriminant analysis (PLS-DA), a frequently used supervised classification method, was applied to differentiate between degradation states of bone samples. PLS-DA results obtained in this study confirmed that changes derived from different burning conditions were associated with transformations in the mineral part of the bones. Accordingly, carbonized bones can be differentiated from cremated bones. Class assignment of bone samples with uncertain thermal conditions in dependence on their elemental composition has shown to be feasible. Consequently, for biochemical-archaeological studies the analysis and statistical classification of carbonized and cremated archaeological bones, as well as those exposed to unknown thermal conditions together with experiments in modern bones, are recommended.     

Burnt bones and teeth: an experimental study of color,morphology, crystal structure and shrinkage

Burnt osteological materials are one focus of interest in forensic, archaeological, and palaeontological studies. We document the effects of experimental, controlled heating on a sample of modern bones and teeth from sheep and goats. Four aspects of heating specimens to between 20 and 940°C were considered: color, microscopic morphology, crystalline structure and shrinkage. Our results show that changes in both color and microscopic morphology of burnt bones and teeth can be divided into five stages each of which is typical of a particular temperature range, although the stages based on color do not correlate exactly with those based on micromorphology. These stages can be used to determine (1) if specimens of unknown taphonomic history were burnt, and (2) the maximum temperature reached by those specimens. In addition, powder X-ray diffraction studies show that heating causes an increase in the crystal size of hydroxyapatite, the major inorganic component of bones and teeth. This fact in conjunction with the microscopic morphology can be used to confirm deduced heating to 645°C or more. The data on shrinkage are analyzed to yield a polynomial expression that summarizes percentage shrinkage as a function of the maximum temperature reached by bones. Thus, the original size of specimens can be reconstructed within limits since the maximum temperature reached by the bones can be deduced on the basis of color, microscopic morphology and/or powder X-ray diffraction patterns. Finally, because there is a discrepancy between the maximum heating device temperature and the maximum specimen temperature, caution must be exercised in distinguishing between the effects of man made and natural fires.     

Burning damage and small-mammal human consumption in Quebrada del Real 1 (Cordoba, Argentina): an experimental approach

The zooarchaeological study of small-vertebrate consumption requires a taphonomical approach to differentiate animal bones that were incidentally incorporated from those that were intentionally exploited in the past human subsistence. In order to make this distinction, the relationship between archaeological small-rodent burned bones and prehistoric human behavior was explored using an experimental cooking study as a modern analogue. During the cooking experiment the entire carcasses of three guinea pigs (Cavia porcellus) and two yellow-toothed cavies (Galea leucoblephara) were placed in the coals of an open fire that simulate a real campfire, rotating their positions until the meat was completely cooked. Subsequently, the intensity of burning damage and the loss of skeletal elements were analyzed at macroscopical levels. The data was used to identify cooking evidence in the Ctenomyidae and Caviidae rodent bones recovered from Quebrada del Real 1 (ca. 6000-300 BP, Córdoba, Argentina). Remarkable similarities between the archaeological and analogical records were found, including the distinctive burning pattern on the distal extremities of the unmeaty long bones (e.g, radii and tibiae), the high frequency of broken incisor teeth and the loss of autopodium elements. Based on these comparative results, it is suggested that the small-rodent assemblages of QR1 were primary accumulated by humans though butchery, cooking and consumption related activities. Extending this study to other archaeological sites in South America may help to identify the prehistoric bone collectors of these small-animals.     

Deficiencies and challenges in the study of ancient tuberculosis DNA

We explore the standards of research and reporting needed to justify the destructive analysis of archaeological human bone for biomolecular studies of ancient tuberculosis (TB). Acceptable standards in osteological interpretation have been met in some biomolecular papers, but there are also cases where insufficient care has been taken in distinguishing between pathognomonic lesions and those that are ‘consistent with’ a diagnosis of TB. Some biomolecular studies have failed to recognize that archaeological bones might be contaminated with environmental mycobacteria whose DNA could give rise to false positives in polymerase chain reactions directed at members of the Mycobacterium tuberculosis complex. The difficulties of applying spoligotyping to ancient DNA have also been underestimated and conclusions drawn from such analyses are often weakly supported. Assumptions that mycobacterial DNA preserves better than human DNA, and that contamination with modern DNA is less of a problem, has led in some cases to a laxity in research standards with insufficient attention paid to the need to authenticate ancient DNA results. We illustrate our concerns by reference to a recent paper reporting biomolecular detection of ancient TB DNA in skeletons from the eastern Mediterranean Neolithic settlement of Atlit-Yam. We are unconvinced that the skeletal evidence presented in this paper gives sufficient indication of TB to warrant destructive analysis, and we are concerned that during the biomolecular part of the project inadequate attention was paid to the possibility that results might be due to laboratory cross-contamination or to amplification of environmental mycobacterial DNA present in the bones.     

The Impact of Climate Change on an Archaeological Site in the Arctic

Climate change may accelerate the degradation of archaeological sites in the Arctic and lead to a loss of important historical information. This study assesses the current preservation conditions and the processes controlling the physical and chemical stability of the Qajaa kitchen midden in western Greenland. Currently, the site is well protected by low ground temperatures, permafrost and a high water/ice content, keeping the deposits anoxic. Based on 5 years of monitoring data, degradation experiments and model simulation, our results suggest that the combined effects of permafrost thaw, thermal and hydrological erosion and oxygen exposure may lead to substantial loss of archaeological evidence before the end of the 21st century.     

BONE POROSITY AND THE USE OF MERCURY INTRUSION POROSIMETRY IN BONE DIAGENESIS STUDIES*

Porosity measurements made on archaeological bones have revealed very-close relationships between changes in the porosity, remaining protein content and mineral alterations. The results have important implications for models that attempt to quantify the rates and extent of chemical reaction between bone and its geochemical environment. We report here on a novel application of an established technique, mercury intrusion porosimetiy, to investigate in more detail the pore size distribution of archaeological bones. Mercury intrusion porosimetry measures an ‘intermediate’range of bone porosity, ‘mesoporosity’, and produces data which permit the observation of significant structure characteristics in the porosity of modern laboratory altered and diagenetically altered bones.     

The long–term survival of bone: the role of bioerosion

Fossil bones (N = 350) spanning more than 350 million years, and covering a wide range of depositional environments, were studied to compare the distribution of microbial destruction features in fossil bones with previously published data sets of bones of archaeological age. The distribution of bioerosion in fossil bones is very different from that found in bone from archaeological sites. Fossil bones typically show little or no bioerosion. Under normal conditions, if a bone is to survive into the fossil record, then rapid bioerosion must be prevented (or halted). This conclusion suggests that early post mortem processes,such as the mode of death, influence the potential of any bone to survive into deep time.