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The influence of elastic properties on finite-element analysis was investigated using a finite-element model of a Macaca fascicularisskull. Four finite-element analyses were performed in which the model was assigned different sets of elastic properties. In analysis 1, elastic properties were modeled isotropically using published data obtained from human limb bones. Analyses 2–4 used data obtained from skulls of a closely allied species, M. mulatta, but varied as to how those data were incorporated into the model. In analysis 2, the model was assigned a single set of isotropic elastic properties. In analysis 3, each region within the model was assigned its own set of isotropic elastic properties. Finally, in analysis 4, each region received its own set of orthotropic elastic properties. Although a qualitative assessment indicates that the locations of strain concentrations across the model are broadly similar in all analyses, a quantitative assessment of strain indicates some differences between the analyses. When strain data from the finite-element analyses were compared to strain data derived from in vivo experiments, it was found that the model deformed most realistically using the orthotropic elastic properties employed in analysis 4. Results suggest that finite-element analyses can be adversely affected when elastic properties are modeled imprecisely, and that modelers should attempt to obtain elastic properties data about the species and skeletal elements that are the subjects of their analyses. © 2005 Wiley-Liss, Inc.

Our work on a finite element model of the skull of Macacaaims to investigate the functional significance of specific features of primate skulls and to determine to which of the input variables (elastic properties, muscle forces) the model behavior is most sensitive. Estimates of muscle forces acting on the model are derived from estimates of physiological cross-sectional areas (PCSAs) of the jaw muscles scaled by relative electromyographic (EMG) amplitudes recorded in vivo. In this study, the behavior of the model was measured under different assumptions regarding the PCSAs of the jaw muscles and the latency between EMG activity in those muscles and the resulting force production. Thirty-six different loading regimes were applied to the model using four different PCSA sets and nine different PCSA scaling parameters. The four PCSA sets were derived from three different macaque species and one genus average, and the scaling parameters were either EMGs from 10, 20, 30, 40, 50 and 60 msec prior to peak bite force, or simply 100%, 50%, or 25% of peak muscle force. Principal coordinates analysis was used to compare the deformations of the model produced by the 36 loading regimes. Strain data from selected sites on the model were also compared with in vivo bone strain data. The results revealed that when varying the external muscle forces within these boundaries, the majority of the variation in model behavior is attributable to variation in the overall magnitude rather than the relative amount of muscle force generated by each muscle. Once this magnitude-related variation in model deformation was accounted for, significant variation was attributable to differences in relative muscle recruitment between working and balancing sides. Strain orientations at selected sites showed little variation across loading experiments compared with variation documented in vivo. These data suggest that in order to create an accurate and valid finite element model of the behavior of the primate skull at a particular instant during feeding, it is important to include estimates of the relative recruitment levels of the masticatory muscles. However, a lot can be learned about patterns of skull deformation, in fossil species for example, by applying external forces proportional to the estimated relative PCSAs of the jaw adductors. © 2005 Wiley-Liss, Inc.

This article reviews the fundamental principles of the finite element method and the three basic steps (model creation, solution, and validation and interpretation) involved in using it to examine structural mechanics. Validation is a critical step in the analysis, without which researchers cannot evaluate the extent to which the model represents or is relevant to the real biological condition. We discuss the method's considerable potential as a tool to test biomechanical hypotheses, and major hurdles involved in doing so reliably, from the perspective of researchers interested in functional morphology and paleontology. We conclude with a case study to illustrate how researchers deal with many of the factors and assumptions involved in finite element analysis. © 2005 Wiley-Liss, Inc.

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This review begins by setting out the context and the scope of human evolution. Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so‐called ‘common hominin ancestor’, and its only extant member is Homo sapiens. This clade contains all the species more closely‐related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini. The rest of the review sets out the formal nomenclature, history of discovery, and information about the characteristic morphology, and its behavioural implications, of the species presently included in the human clade. The taxa are considered within their assigned genera, beginning with the most primitive and finishing with Homo. Within genera, species are presented in order of geological age. The entries conclude with a list of the more important items of fossil evidence, and a summary of relevant taxonomic issues.

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New fossils recovered from the Pliocene of Ethiopia and attributed to Australopithecus afarensis (White et al., 1993; Kimbel et al., 1994) provide an opportunity to reassess size variation and sexual dimorphism in jaws and limb bones of these early hominids. In this study two related questions are addressed using exact randomization methods. First, is it possible to observe the fossil size range within samples of modern hominoids? Second, and moving beyond minimum/maximum possibilities to probabilities, what is the likelihood of sampling such differences in extant hominoids? Fossil minimum/maximum ranges in size and shape are defined by linear measurements from mandibular specimens A.L. 444-2b vs. A.L. 207-13, humeri MAK-VP-1/3 vs. A.L. 288-lm, and the proximal femora A.L. 333-3 vs. A.L. 288-lap. Modern reference samples include gorillas, orang-utans, common chimpanzees and several human groups (all of known sex). All possible pairwise contrasts (in size ratios and average Euclidean distances) are computed within each sample [e.g. within a sample of 50 gorillas (25 males, 25 females) 1225 total contrasts are possible of which 625 are opposite sex contrasts], and the probability of finding a difference as great as that seen in the fossil pair is noted. The maximum observed size (sex) difference in the fossil mandibles, humeri and proximal femora is either rare or not observed in human and chimpanzee samples, is rare to uncommon in orang-utans, and is unusual even in gorillas. Specimens recovered in the future will undoubtedly increase the fossil ranges, and thereby further reduce the probabilities of matching such differences in modern taxa. These results could imply that multiple taxa exist within the fossil assemblage. If the fossils from Hadar and Maka (and Laetoli) are assumed instead to be from one sexually dimorphic species, then the degree of sexual dimorphism of A. afarensis would have been at least as extreme as that of the most dimorphic living apes, the gorilla and orang-utan. It follows that a strictly monogamous social structure would have been highly unlikely. Copyright 1995, 1999 Academic Press