Faculty Bibliography

The structure of growth patterns on fish scales is characteristically anisotropic: the number of circuli and their widths significantly vary with the direction of measurement. We show, however, that because of anisotropy, fish scale growth rate variability can be described in fuzzy terms. The index of structural anisotropy is introduced, which serves as a measure of the fuzziness of growth-rate quantification. A discrete model of fish scale incremental pattern is proposed, which takes into account the incremental structure in 2D. This model is based on a representation of the fish scale pattern as a relay network, taking anisotropy in the form of discontinuities and convergences of incremental structural elements into account, and the widths of growth increments in different directions. The model is used to formalize procedures necessary for the quantification of fish scale growth rate. The capability of the model for analysing objects with similar structural attributes as found in fish scale incremental patterns, such as those found in coral, otoliths, shells, and bones, is demonstrated. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved

Bromage reviews Bioarchaeology: Interpreting Behavior from the Human Skeleton by Clark Spencer Larsen

Bone exhibits positive form birefringence dominated by and dependent upon the orientation of its collagen. The biomechanical efficacy of bone as a tissue is largely determined by collagen fibers of preferred orientation and distribution (and corresponding orientation of mineral crystallites), and evidence is accumulating to demonstrate that this efficacy extends to function at the organ level. This study has three aims. The first is to provide a Background to the study of circularly polarized light (CPL) investigations of collagen fiber orientation in bone. The significance of preferred collagen fiber orientation in bone, linearly polarized light and CPL imaging principles, and a short history of CPL studies of mammalian functional histology are reviewed. The second is to describe, in some detail, methodological considerations relating to specimen preparation and imaging appropriate for the quantitative analysis of preferentially oriented collagen. These include section transparency, section thickness, the uniformity of the illuminating system, and CPL paraphernalia. Finally, we describe a grey-level standard useful for quantitative CPL, based upon mineralized turkey tendon, which shall be provided to investigators upon request. When due consideration is paid to specimen preparation and imaging conditions, quantitative assessment of collagen fiber orientation provides insight into the effects of mechanical loading on the skeleton

One of several microstructural variables known to affect the mechanical properties of bone is the degree of mineralization of bone matrix. The aim of this study was to examine mineralization density, and its variability with age and sex, from a biomechanical perspective. Histological sections, prepared from mid-shaft femora obtained at autopsy from 40 individuals, were imaged using quantitative backscattered electron microscopy. Each cross-section montage was divided into 48 segments according to anatomical position. Mean grey-level values were quantified for each segment. One-way ANOVA with Tukey HSD post hoc tests were used to test for differences in mineralization between segments, age groups and sexes. Results showed a decrease in overall degree of mineralization density with adult age, but an increase in its coefficient of variation. Degree of mineralization was significantly lower in the periosteal third of the cortex, particularly in the antero-lateral aspect. This pattern was most prevalent amongst the youngest individuals in the sample. Whereas males between ages 45-64 years had a higher average degree of mineralization than females, the opposite was true of the older age group. Mineralization significantly decreased between middle and older age groups in males, but not in females. Despite limited consistencies in the location of high and low average mineralization bone through the cortex, the degree of interindividual variation, even within a single age and sex group, overwhelmed population level trends. The patterns of variability identified in this study are consistent with results of an analysis of collagen fibre orientation using the same sample material

Collagen fiber orientation is one aspect of the microstructure of bone that influences its mechanical properties. While the spatial distribution of preferentially oriented collagen is hypothesized to reflect the effects of loading during the process of aging, its variability in a modern human sample is essentially unknown. In a large sample (n = 67) of autopsied adults, the variability of collagen fiber orientation in the mid-shaft femur was examined in relation to age and sex. Montaged images of entire 100 microm thick cross-sections were obtained using circularly polarized light microscopy (CPLM) under standardized illuminating conditions. An automated image-analyzing routine divided images into 48 segments according to anatomical position. Average gray values (varying with orientation) were quantified for each segment, and one-way ANOVA with Tukey HSD post hoc tests were applied to assess differences between segments. Collagen fiber orientation appeared to be nonrandomly distributed across the mid-shaft femur sample; however, no single 'human' pattern was identified. Individual variation, unexplainable by age, sex, or body size, exceeded population-level trends. Differences between age and sex groups suggest there is a strong correspondence between collagen fiber orientation and tissue-type distributions. The minimal consistencies demonstrated here may reflect mechanical forces induced at the femoral mid-shaft. However, the myriad of other factors that may influence collagen fiber orientation patterning, including growth trajectories, metabolic and nutritional status, and disease states, must be explored further. Only then, in conjunction with studies of other structural and material properties of bone, will we be able to elucidate the linkages between microstructure and functional adaptation in the human mid-shaft femur

Remains of early Homo and Paranthropus have been recovered from two contemporaneous sites (Uraha and Malema) in the "Hominid Corridor" in Northern Malawi (Chiwondo Beds). Faunal dating suggests an age of 2.5-2.3 Ma for both hominids. The two specimens, a mandible attributed to Homo rudolfensis(UR 501 from Uraha), and a maxillary fragment of Paranthropus boisci. (RC 911 from Malema) known only from eastern Africa, represent the southernmost known distribution of these taxa. The biogeographic significance of these hominids from the Malawi-Rift lay in their association with the eastern African endemic animal group. Biogeographic variation in south-eastern Africa may be linked to habitat change occurring due to climate change, with maximum change occurring around 2.5 Ma.