Identification of archaeologically recovered vertebrate specimens is fundamental to all subsequent zooarchaeological analysis. The task begins with osteological identification within the framework of zoological classification, and also includes recognizing the many possible factors that can influence how our study assemblage preserved (see Osteological Methods). During identification, we make additional observations that help us to interpret the circumstances surrounding assemblage accumulation and deposition, subsequent burial, and field recovery. Although many of these clues may eventually lead to equifinal determinations, they remain fundamental to the reliability and validity of inferences that we generate about past subsistence and palaeoecology.
Osteological Identification
Osteological identification is accomplished by comparing unidentified bone specimens with identified skeletal materials. Archaeologists can consult major museum research collections which are usually developed by and for zoologists, or they might have access to purpose-built collections. In either case, using comparative skeletal material to identify an unknown specimen is preferable to depending exclusively on illustrations in published guides. The different perspectives that three-dimensional bone elements provide are always superior for purposes of identification, especially as most archaeological specimens are fragmented. However, osteological guides can be useful for presorting specimens by expediting subsequent verification in the comparative collection.
Identification is multifaceted and begins by locating the specimen within the skeletal system. Although a relatively straightforward exercise, identification can be obscured by fragmentation. Fragmented bone specimens can be too small to identify to any level of acuity, and it is frequently the case that larger animals produce larger unidentifiable fragmented bone specimens. Skeletal elements are variably dense throughout their structure, and portions that are relatively resistant to fragmentation can retain identifiable landmarks. Some elements with fewer diagnostic features are intrinsically difficult to identify, regardless of their preserved state. Teeth are particularly durable and highly identifiable. In the case of a fragmented specimen, its directional location on the element when compared to anatomical position in medial/ lateral, dorsal/ventral, and cranial/caudal orientation is noted where possible. Bilateral symmetry in most vertebrates also permits left and right sides to be differentiated for many elements (see Bioarchaeology).
Zooarchaeologists organize their identifications within a comprehensive and ordered taxonomic system. The hierarchical nature of zoological classification can accommodate the relative specificity to which any specimen can be identified, depending upon the kind of element and organism from which it originated and its associated state of preservation. With the exception of skull anatomy and dentition, zoological systematists generally base their inferences about natural populations on various criteria that do not preserve in the archaeological record. Teeth, in particular, are believed to represent genetically derived morphology, and to reflect diet and habitat. As a result, certain elements within the vertebrate plan, like durable dental material, are diagnostically more useful than others for higher resolution identification. Depending on their relative diagnostic utility and state of preservation, most vertebrate specimens can be identified within an ascending scale of acuity approximating species, genus, family, order, and class, in addition to using modifying attributes like size (e. g., small canid, large mammal).
Although these interrelated factors clearly influence the relative specificity to which any specimen can be identified, the acuity of identification is also determined by other less obvious factors. Certain vertebrates are simply easier to identify because they are better studied, or because their skeletal morphology is relatively rare or unique. The skeletons of many highly speciose vertebrate taxa can be indistinguishable from one another. Often, differentiating between commonly indistinguishable skeletons is presumed because of associated spatial or temporal context. For example, a specimen that could equally represent a domesticated cow or wild bison might be identified as either because its associated context is of an age where domesticates are unexpected, or because it was recovered in an area where bison are unlikely to have lived. Size differences may be similarly used; for example, a large canid specimen may be identified as a wolf because it is large, or as a fox because it is small. Also, the reliability of an identification may be directly related to the spatial, temporal, or demographic completeness of the reference collection, or simply as a factor of the relative experience of the analyst. Zoological identification is never immutable; taxonomic adjustments necessitated by evolutionary change or subsequent reclassification are to be expected.
Further osteological observations of preserved specimens are necessary for establishing the sex of the animal or estimating its age at death. This evidence is useful for inferences about subsistence and ecology. In some cases, sex can be determined by the presence of sex-specific characteristics on certain bone elements, or through the use of measurements which might differentiate between sexes on the basis of size differences. Age at death can be estimated by comparing the relative fusion of growth centers and eruption of teeth with published fusion/eruption schedules. Occlusal wear on teeth or the accretion of incremental growth in many elements can be used to establish age at death, or along with context, season of death. Aspects of individual health can be assessed by recording pathological or age-related change in bone. In some instances, overall shape and size, or the presence/absence of specific structures can be used as evidence for animal domestication. Inferences about the early domestication of some taxa are substantiated by noting proportionate size changes through time, using standardized measurements of specified skeletal elements.
Identification of Recovery Bias
It is important to understand how different field recovery techniques have affected the numbers, kinds, and condition of bone specimens in the sample assemblage. The reliability of our inferences depends on whether the presence/absence, relative abundance, or condition of any specimen in the sample is simply related to the way that the sample assemblage was recovered in the field.
During identification, basic physical characteristics of each specimen are recorded. In the absence of more specific evidence, specimen weight can supplement the simple numbers of identified specimens (NISP) as a proxy for bone volume. Although a laborious task, measuring the maximum length, width, and depth of each fragment provides a better approximation of bone volume, and can be useful for empirically estimating how field recovery techniques may have affected the sample assemblage. The volume of bone, overall abundance, and proportion of small fragments increase with use of smaller aperture screens and water separation techniques. What is the relationship between specimen size and the accuracy to which it can be identified? Is a proportionate increase or decrease of small and unidentifiable bone simply a factor of the method used to recover the sample in the field? Is the sample of identified specimens affected by the potential gain or loss of diagnostic specimens of smaller animals that can be easily missed in coarsegrained field recovery? If we can understand these relationships, we should be able to gauge the effect of recovery in differently sampled contexts, and adjust our inferences accordingly.
Specimen recovery in the field, and subsequent processing and handling for identification, can lead to fragmentation. Bone breakage is relevant to our inferences only if it was not the recent product of archaeological recovery. Bone specimens often break during excavation and exposure and can be fragmented through screening, water separation, and rough handling. Fortunately, the freshness of these breaks can be identified by distinct coloration, which also facilitates the necessary but often labor-intensive task of refitting what were once larger specimens.
Identification of Assemblage Accumulation
The reliability and validity of our inferences about past subsistence and ecology depend upon understanding how, and under what circumstances, the assemblage was originally accumulated. If we can demonstrate that a bone assemblage was originally accumulated by humans for their consumption, then we can establish its potential relevance for subsistence studies. The identified animals within this assemblage may also have some relevance for palaeoecological inference; however, it must be understood that they represent a collection that is biased according to the preferences of its human accumulators. This assemblage does not adequately represent the range of animals that existed in and around the site at the time of deposition, and if originally introduced from an entirely different context, would be completely inappropriate for inferences about local palaeoecol-ogy. If we can prove that a bone assemblage was not originally accumulated by humans, its relevance to questions about human subsistence is usually moot. However, its relevance for inferences about local palaeoecology can depend upon identifying who the original accumulator was and recognizing the biases that it can introduce into assemblage composition.
Human accumulation Identifying how the assemblage was originally accumulated begins with archaeological context, and involves preserved evidence on bone specimens. Observations supporting human accumulation can include evidence associated with the cultural butchery and consumption of animals. Resulting modifications can involve bone breakage, marks left by tools, and carcass disarticulation. Zooarchaeologists note the anatomical location of breakage, morphology of the actual break, nature of breakage surfaces, and evidence for what may have caused the breakage. Nevertheless, supporting evidence is often ambiguous because not all the preserved modifications are necessarily unique to any specific bone-modifying event. Patterns of breakage often tend to be governed by properties of the bone that was broken rather than the event responsible for its breakage. We examine in detail the location, orientation, function, and morphology of butchery marks potentially left by human tools. In particular, various attributes of mark morphology, including its shape in various perspectives, frequency, and orientation are heavily relied upon in human butchery studies. Nevertheless, human butchery marks tend to be rare, especially as they are often incidental to their purpose. They can also be inconsistent to their original purpose, and prone to idiosyncrasy. Patterning in disarticulation, on its own, is unreliable for identifying who or what modified a carcass because this tends to be controlled by anatomical variables, rather than characteristics unique to any specific event. Reliance on any or all of these clues to establish human involvement is best achieved through multiple lines of evidence and archaeological context.
Heat modification is often used as a criterion of human accumulation for the purpose of consumption; however, equifinality is always possible because human behavior is not a necessary prerequisite for burned bones. Heat modification can occur after assemblage deposition or may be entirely incidental to human involvement. Furthermore, although heat is regularly used in the human consumption of animal products, the actual burning of bone is commonly a factor of refuse discard and deposition rather than food consumption. Cultural heat modification, such as boiling in pots or roasting deboned meat, may leave no burned bones. Nonetheless, during specimen identification, zooarchaeologists record evidence for the relative intensity of, and length of exposure to, heat. This can be inferred from coloration which is associated with the degree to which organic content within bone has combusted. Empirically derived comparisons of coloration and fire temperature are available in the literature. The patterning of heat modification on bone specimens can be used as evidence for purposive human use, particularly if consistently associated with specific anatomical areas or related to certain identifiable techniques (e. g., spit roasting). Heat modification in direct association with breakage and verifiable tool marks can be relevant for bone modification activities like human marrow extraction or bone tool manufacture.
Modified tools and digested bone constitute direct, albeit relatively rare, evidence for purposive human use. Wherever possible, zooarchaeologists note the element and kind of animal from which the tool was made, any surficial modification that may have resulted from use, and its possible function. Bone tools are often treated separately from other specimens in the assemblage. Humans do not regularly ingest bone that can pass through the digestive tract and preserve in a state which is readily identifiable to any great precision. In the rare event that this might happen, unambiguously establishing that it was eaten and expelled by a human is difficult. One obvious exception is the preservation of dietary bone in copro-lites, which would necessarily include diagnostic fragments of smaller vertebrates that may have been ingested relatively whole or with minimal mastication. Specific characteristics of the coprolite and its archaeological context can be used to identify its origin (see Coprolite Analysis).
Nonhuman accumulation Bone assemblages are frequently accumulated, either whole or in part, by events other than human activity. We must be able to distinguish the different accumulation histories that may be represented in any assemblage. Nonhuman animals often impart vertebrate specimens as byproducts of their consumption activities. Larger carnivores can compete with humans for larger prey sources, and their accumulations can be identified through marks left on bone specimens during the course of reducing prey carcasses for consumption. As with human tools, various attributes of mark morphology, including shape in various perspectives, frequency, and orientation are heavily relied upon to identify large carnivore accumulations. Tooth marks, in particular, are much more common on comminuted bone, and can be identified through comparison with bone damage observed in actualistic studies of carnivore feeding. Bone specimens that have been swallowed and subsequently passed through digestive tracts can also be identified on the basis of visible digestive modification. Sometimes, the producer of the coprolite can be identified from characteristics of the scat, its contents, and archaeological context. However, in some temporal or spatial contexts, positive identification of the animal accumulator can be difficult, especially where different predators share similarities in masticatory apparatus, consumption behavior, and digestive properties.
Microvertebrate assemblages are commonly accumulated by nonhuman carnivores. These assemblages invariably consist of small-bodied prey that was swallowed either whole or with minimal mastication. Denning carnivores can deposit scats that include bone which passed through the digestive tract, and many roosting owls and raptors deposit undigested bone material in regurgitated pellets. In either case, digestive modification can be identified on bone and tooth specimens and compared to results of actualistic feeding studies of various carnivores. When preserved, adhering pellet or scat material can be used to identify the source of accumulation. Zooarchaeologists also rely on the relative proportions of surviving skeletal elements and associated archaeological context to corroborate their interpretations; however, these are not immune to ambiguity.
Vertebrate assemblages are also deposited as the by-product of bone collection and consumption by noncarnivores. Bone modification as a result of consumption for mineral nutrients has been studied in certain animals. Other animals such as wood rats or ants are also known to collect bone. Many rodents collect and modify bone through a need to file their ever-growing teeth. Distinct tooth marks, often of different color from the rest of the bone surface, can be identifiable. The location of these gnaw marks is also important as they tend to be restricted to accessible edges of bone specimens. The relative size of bone specimens, and archaeological context, can also offer clues about the identity of the bone collector.
Potential concentrations of vertebrate skeletal material in buried contexts can be deposited through the death and decay of animals that frequent underground substrates. These assemblages can become contextually associated with archaeological materials deposited through other means via intrusive burrowing. Differential coloration of the intrusive specimen may be used as evidence, especially in cases where the intrusion occurred after deposition of the rest of the assemblage. Associated clues involve skeletal completeness and archaeological context, and most notably whether or not the specimens are those of a fossorial animal. Accidental entrapment and the subsequent death and decay of soft tissue can also introduce vertebrate specimens into certain archaeological contexts. Here again, zooarchaeologists use similar clues such as specimen coloration, relative skeletal completeness, ecology of identified animals, and archaeological context to support their interpretations.
Bone assemblages can be accumulated and modified through fluvial transport, as moving water can sort different elements according to their respective shape and structural density. Certain skeletal elements are prone to hydrodynamic transport under lower velocity conditions and are capable of dispersal over longer distances. Characterizations of specimen shape can be examined by manipulating maximum length, width, and thickness measurements, and the relative structural density of bone portions is published for many taxa. Specimens should also be examined for abrasion that might have resulted from modification through tumbling action in moving water; however, events other than water action can also abrade bone surfaces. Archaeological context can also be taken into account when assessing hydrodynamic transport, particularly through studying surrounding sediment matrix and noting patterns in specimen orientation.
Identification of Modification after Deposition
After deposition and before burial, accumulations are prone to continued modification by addition, subtraction, and spatial rearrangement. Accumulators are also dispersers. Assemblages can be modified by the addition of new specimens, or simply through increased fragmentation which increases sample size. Exposed bone accumulations can be selectively scavenged or completely redeposited through natural and cultural dispersal. Recognizing the sequential position of a recovered sample within a complex tapho-nomic history can be very difficult. In some cases, the analyst might be able to establish a relative succession of events by observing any preserved overlap of relevant clues. For example, a human butchery scar that underlies a carnivore tooth puncture can reveal important evidence about the order of events within a longer taphonomic sequence.
Surface assemblages are exposed to atmospheric weathering, which can lead to further destruction, particularly through desiccation. Interrelated factors, including the intensity of atmospheric processes, length of exposure, local environmental conditions, the kind of element that is exposed, and from what kind of animal it originates, can affect both the degree and speed of weathering. Where appropriate, zooarchaeologists typically note arbitrary stages of weathering within a continuum from fresh to disintegration, which are based on actualistic studies of cracking, flaking and subcortical bone exposure.
Exposed bone material can be subjected to trampling by humans and nonhumans alike. Depending upon the substrate, trampling can bury specimens in loose sediment or displace them horizontally in compact sediment. Trampling can further modify bone through fragmentation and abrasion. Experiments have demonstrated that scratch marks can be produced through trampling; however, they can be morphologically difficult to distinguish from damage produced by other agents. In these cases, their orientation and positioning on bone specimens are examined for corroboration. Bones can be modified by acid secretions from roots and fungus which leave distinct dendritic ‘root etching’ patterns both prior to and after burial.
After burial, bone assemblages can be physically and spatially altered, subtracted from, or added to. Sediment overburden can modify buried bone through deformation and fragmentation. Postburial weathering continues as bone material is disintegrated by physical and chemical agents in the burial matrix. Modification of buried bone material is influenced by the burial environment and factors intrinsic to skeletal material. Size, shape, fragmentation, and porosity of the buried specimen, along with soil chemistry, water, temperature, and microbial activity, all contribute to the rate and extent of subsurface weathering. The effects of diagenesis, which involves the physical and chemical alteration of buried bone material, must be taken into account by the zooarchaeologist. Any evidence for the dissolution of bone material in the burial matrix is noted, as are mineral concretions adhering to bone surfaces. Postburial breakage may be identified through fracture morphology, fracture coloration, fragment size, conjoin-ability, and archaeological context.
World History
