restricted access Chapter 6. Bone Structure and Taphonomic Processes
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PART III 89 The interpretation of vertebrate skeletal remains is a significant component in our understanding of the global archaeological record. This significance is evident not only in the abundance of osseous material in many archaeological assemblages, but also in this material ’s ability to provide insights or meaning relative to the activities, social structures, belief systems, technological adaptations, health and dietary conditions, and environmental constraints of early cultures. The ability of bones to convey information in this sense is often dictated by intrasite context as well as the form and degree of modification they have been subjected to. Bone has been put to a variety of uses through time, and these different uses frequently manifest archaeologically in breakage or modification patterns that are distinct from patterns of noncultural modification. Modification and breakage can also signify the use of bone for activities such as tool manufacture , butchery, marrow or grease extraction, fuel, and dwelling construction. As an initial step in using bone to decipher archaeological enigmas, an understanding of the structural characteristics of bone relative to fracture dynamics is necessary. Few investigators have addressed the pertinent histological literature relevant to the archaeological context. Bonnichsen (1979, 1983a), E. Johnson (1985), Lyman (1994:70–113), and Morlan (1980) provide thoughtful reviews of the physical properties of bone; however, Morlan (1980) rejects the importance of microscopic factors in his synthesis. Bone Structure The microscopic and macroscopic arrangements of components and the physiological dynamics of mammalian bone are considerably different from those of cryptocrystalline materials. Therefore, the parameters governing the fracturing and flaking of lithics differ from those governing bone. Because bone fractures differently from rock, it is necessary to understand the macroscopic, microscopic, and ultrastructural composition and histogenesis of bone. Histopathological reviews of the structural and functional characteristics of bone are presented in Andrew and Hickman (1974), Aurbach and Phang (1980), Bloom and Fawcett (1975), Currey (1984, 2006), and Sweeney et al. (1965). Bourne (1976) presents more detailed reviews pertaining to the biochemistry of bone. The following discussion draws upon these works. Macroscopic Structure of Bone Tissue Bone tissue consists of cells, fibers, and ground substances, not unlike other connective tissues (fibrous connective tissue, elastic connective tissue, elastic cartilage, and hyaline cartilage), but it does possess a unique calcified extracellular component. The hard, unyielding nature of bone makes it functionally suited for its supportive and protective roles. In addition to those mechanical functions, bone tissue functions as a reservoir for metabolic calcium and phosphate ions. It is the exchange of these ions that contributes to the reorganization and remodeling of bone. Bone has a combination of physical properties that ensure the greatest strength along with great economy of material and minimal weight (Bloom and Fawcett 1975:244). Its high tensile and compressive strength and elastic characteristics are provided by individual components that, when combined, confer unique properties to the composite tissue not possessed by the constituent parts. Two forms of bone, substantia spongiosa (cancellous) and substantia compacta (compact), demonstrate different arrangements of osseous materials. The spongiosa is a Bone Structure and Taphonomic Processes chapter six L. Adrien Hannus 90 Chapter Six trabecular lattice labyrinth, whereas the compacta is a continuousmass ;thetwoformsgradeintooneanotherwithout a precise boundary (Bloom and Fawcett 1975:245). These two forms of bone vary as to the arrangement of lamellae making up their structure; this is described in greater detail in the section below on microscopic structure. The five types of bone—long bones, short bones, flat bones, irregular bones, and sesamoid bones—generally demonstrate a peripheral cortex of compact bone and an inner arrangement of cancellous bone. Long bones (ossa longa) consist of a diaphyseal, or shaft-like, portion comprising a compact bone cylinder with an inner medullary cavity occupied by myeloid tissues (fig. 42). The two epiphyseal portions, or ends, of the long bone comprise a thin peripheral cortex of compact bone and an inert core of cancellous bone. The trabecular labyrinth of the epiphyseal cancellous bone is continuous with the medullary cavity of the diaphysis (fig. 43). Cancellous bone is developed where the greatest stress occurs. An age-dependent feature of long bone is the presence of a cartilaginous epiphyseal plate, the origin of which is the convergence of ossification fronts during the histogenesis of the bone tissue; this process is described in greater detail in the section on histogenesis. The osteogenic potential of the converging ossification fronts is the metaphyseal portion, comprising a transitional cancellous bone and the epiphyseal plate. On the articular surfaces of the epiphyses is...