Fossil Homo femur from Berg Aukas, northern Namibia

Cranial muscle markers: a preliminary examination of size, sex, and age effects

Most muscle marker research consists of post-cranial analyses, but some researchers examine crania to reconstruct activities. Regardless of bones examined, anthropologists know of some of the complexities surrounding muscle marker development. Here, posterior cranial muscle markers are analyzed to determine whether they are useful in reconstructing activities by examining effects that may hinder reconstructions. Additionally, upper limb muscle markers and humeral cross-sectional robusticity variables are correlated with cranial muscle markers to determine if robust individuals are generally robust due to the synergistic effects of muscle use. Cranial muscle markers of 65 prehistoric California Amerinds are scored using a five-point observer rating scale. Body mass is calculated from femoral head size; maximum cranial length and breadth are measured with a spreading caliper; and age and sex are determined through standard procedures. Upper limb muscle markers are scored on seven sites using two dimensions within a seven-point scale. Cross-sectional properties are calculated from biplanar humeral radiographs. Aggregates are created for cranial muscle markers, upper limb muscle markers, and cross-sectional robusticity. Cranial muscle markers correlate significantly with cranial length, r=0.25 and cross-sectional robusticity of humerus, r=0.29; P's<0.05. All variables differed between sexes (Mann-Whitney=31.00-307.50, P's<0.01). Results imply that some differences in cranial muscle markers are related to size; however, individuals with well-developed cranial muscle markers have greater upper limb robusticity possibly due to activity patterns. Sex differences remained after size controls and may relate to activity differences.

The shape of the early hominin proximal femur

Postcranial skeletal variation among Plio-Pleistocene hominins has implications for taxonomy and locomotor adaptation. Although sample size constraints make interspecific comparisons difficult, postcranial differences between Australopithecus afarensis and Australopithecus africanus have been reported (McHenry and Berger: J Hum Evol 35 1998 1-22; Richmond et al.: J Hum Evol 43 [2002] 529-548; Green et al.: J Hum Evol 52 2007 187-200). Additional evidence indicates that the early members of the genus Homo show morphology like recent humans (e.g., Walker and Leakey: The Nariokotome Homo erectus skeleton. Cambridge: Harvard, 1993). Using a larger fossil sample than previous studies and novel methods, the early hominin proximal femur is newly examined to determine whether new data alter the current view of femoral evolution and inform the issue of interspecific morphological variation among australopiths. Two- and three-dimensional data are collected from large samples of recent humans, Pan, Gorilla, and Pongo and original fossil femora of Australopithecus, Paranthropus, and femora of African fossil Homo. The size-adjusted shape data are analyzed using principal components, thin plate spline analysis, and canonical variate analysis to assess shape variation. The results indicate that femora of fossil Homo are most similar to modern humans but share a low neck-shaft angle (NSA) with australopiths. Australopiths as a group have ape-like greater trochanter morphology. A. afarensis differs from P. robustus and A. africanus in attributes of the neck and NSA. However, interspecific femoral variation is low and australopiths are generally morphologically similar. Although the differences are not dramatic, when considered in combination with other postcranial evidence, the adaptive differences among australopiths in craniodental morphology may have parallels in the postcranium.

A description of the Omo I postcranial skeleton, including newly discovered fossils

Recent fieldwork in the Kibish Formation has expanded our knowledge of the geological, archaeological, and faunal context of the Omo I skeleton, the earliest known anatomically modern human. In the course of this fieldwork, several additional fragments of the skeleton were recovered: a middle manual phalanx, a distal manual phalanx, a right talus, a large and a small fragment of the left os coxae, a portion of the distal diaphysis of the right femur that conjoins with the distal epiphysis recovered in 1967, and a costal fragment. Some researchers have described the original postcranial fragments of Omo I as anatomically modern but have noted that a variety of aspects of the specimen's morphology depart from the usual anatomy of many recent populations. Reanalysis confirms this conclusion. Some of the unusual features in Omo I--a medially facing radial tuberosity, a laterally flaring facet on the talus for the lateral malleolus, and reduced dorsovolar curvature of the base of metacarpal I--are shared with Neandertals, some early modern humans from Skhul and Qafzeh, and some individuals from the European Gravettian, raising the possibility that Eurasian early modern humans inherited these features from an African predecessor rather than Neandertals. The fragment of the os coxae does not unambiguously diagnose Omo I's sex: the greater sciatic notch is intermediate in form, the acetabulum is large (male?), and a preauricular sulcus is present (female?). The preserved portion of the left humerus suggests that Omo I was quite tall, perhaps 178-182 cm, but the first metatarsal suggests a shorter stature of 162-173 cm. The morphology of the auricular surface of the os coxae suggests a young adult age.

A critique of the chronometric evidence for hominid fossils: I. Africa and the Near East 500-50 ka

The chronometric dating evidence for all hominid fossils from Africa and the Near East that have previously been dated to 500-50 ka is critically assessed using the concept of chronometric hygiene, and these dates are revised using Bayesian statistical analyses where possible. Sixteen relevant hominid sites lacking chronometric evidence are briefly discussed. Chronometric evidence from 37 sites is assessed in detail. The dates for many hominid fossils are poorly constrained, with a number dated by comparisons of faunal assemblages-a method that does not have good chronological resolution for much of the last million years. For sites with stratigraphic sequences of dates, it is generally possible to refine the dating, but in some cases, the revised chronology is less precise than previous chronologies. Fossils over 200 ka in age tend to be poorly dated, but for the last 200 kyr, dating is better due to the availability of electron-spin-resonance and thermoluminescence dating. Consideration of the chronologies favored by the proponents of the out-of-Africa and multiregional hypotheses of human evolution shows their selectivity. The chronological assessment of the fossils here is compatible with either hypothesis. If evolutionary schemes that do not rely on the morphology of the hominid fossils to decide the sequence of fossils are to be built, then further dating is required, alongside full publication of existing dates.

A re-examination of a human femur found at the Blind River Site, East London, South Africa: Its age, morphology, and breakage pattern

Modern human femoral features might have appeared in the early Middle Stone Age (156 ka to 20 ka) in South Africa, as demonstrated by the recent re-examination of a human femur fossil found at the Blind River Site, East London in the 1930s, if new dating results hold. Two optically stimulated luminescence dates from the relocated original Blind River shallow marine/estuarine deposits that contained the femur gave almost identical ages of ~120 ka, corresponding to the early part of the Last Interglacial (Oxygen Isotope Stage 5). Overall, the slender headless femur is of modern human form. The distal epiphysis bears some typical squatting features, including a newly recognized squatting facet on the anterior wall of the intercondylar fossa. With the typical V-shaped and oblique fracture pattern left by the missing head, the Blind River femur was most likely modified through human activity. But this style is not a cultural trait found in recent South African people. Further study is needed to place this specimen in its due context in the course of human evolution.

Mobility in Central European Late Eneolithic and Early Bronze Age: femoral cross-sectional geometry

Some scholars explain the absence of settlements in the Bohemian and Moravian Late Eneolithic (Corded Ware archaeological culture) as a consequence of pastoral subsistence with a high degree of mobility. However, recent archaeological studies argued that the archaeological record of the Late Eneolithic in Central Europe exhibits evidence for sedentary subsistence with mixed agriculture, similar to the subsequent Early Bronze Age. Because the archaeological data do not allow us to address unambiguously the mobility pattern in these periods, we used cross-sectional analysis of the femoral midshaft to test mobility directly on the human skeletal record. The results of femoral midshaft geometry do not support a high degree of mobility in the Late Eneolithic in Central Europe. This conclusion is supported mainly by no significant differences in male groups between the Late Eneolithic and Early Bronze Age in mechanical robusticity and shape of the femoral midshaft, although Corded Ware males still exhibit the highest absolute mean values of the diaphyseal shape (I(A-P)/I(M-L)) ratio and antero-posterior second moment of area. However, Late Eneolithic females have significantly higher torsional and overall bending rigidity because of a significantly higher medio-lateral second moment of area. This finding cannot be directly linked with a higher degree of long-distance mobility for these females. A significant difference was also found in overall decrease of size parameters of the femoral midshaft cross section for one of the Early Bronze Age samples, the Wieselburger females. Since the decrease of size and mechanical robusticity for Wieselburger females does not correspond with the parameters of Early Bronze Age females, we can expect a mosaic pattern of changes during the Late Eneolithic and Early Bronze Age period, instead of a simple unidirectional (diachronic) change of the mechanical environment.

Thoracic skeletal morphology and high-altitude hypoxia in Andean prehistory

Living humans from the highland Andes exhibit antero-posteriorly and medio-laterally enlarged chests in response to high-altitude hypoxia. This study hypothesizes that morphological responses to high-altitude hypoxia should also be evident in pre-Contact Andean groups. Thoracic skeletal morphology in four groups of human skeletons (N = 347) are compared: two groups from coastal regions (Ancón, Peru, n = 79 and Arica, Chile, n = 123) and two groups from high altitudes (San Pedro de Atacama, Chile, n = 102 and Machu Picchu and Cuzco, Peru, n = 43). Osteometric variables that represent proportions of chest width and depth include sternal and clavicular lengths and breadths and rib length, curvature, and area. Each variable was measured relative to body size, transformed into logarithmic indices, and compared across sex-specific groups using ANOVA and Tukey multiple comparison tests. Atacama highlanders have the largest sternal and clavicular proportions and ribs with the greatest area and least amount of curvature, features that suggest an antero-posteriorly deep and mediolaterally wide thoracic skeleton. Ancón lowlanders exhibit proportions indicating narrower and shallower chests. Machu Picchu and Cuzco males cluster with the other highland group in rib curvature and area at the superior levels of the thorax, whereas chest proportions in Machu Picchu and Cuzco females resemble those of lowlanders. The variation in Machu Picchu and Cuzco males and females is interpreted as the result of population migrations. The presence of morphological traits indicative of enlarged chests in some highland individuals suggests that high-altitude hypoxia was an environmental stressor shaping the biology of highland Andean groups during the pre-Contact period.

Limb length and locomotor biomechanics in the genusHomo: An experimental study

The striking variation in limb proportions within the genus Homo during the Pleistocene has important implications for understanding biomechanics in the later evolution of human bipedalism, because longer limbs and limb segments may increase bending moments about bones and joints. This research tested the hypothesis that long lower limbs and tibiae bring about increases in A-P bending forces on the lower limb during the stance phase of human walking. High-speed 3-D video data, force plates, and motion analysis software were used to analyze the walking gait of 27 modern human subjects. Limb length, as well as absolute and relative tibia length, were tested for associations with a number of kinetic and kinematic variables. Results show that individuals with longer limbs do incur greater bending moments along the lower limb during the first half of stance phase. During the second half of stance, individuals moderate bending moments through a complex of compensatory mechanisms, including keeping the knee in a more extended position. Neither absolute nor relative tibia length had any effect on the kinetic or kinematic variables tested. If these patterns apply to fossil Homo, groups with relatively long limbs (e.g. H. ergaster or early H. sapiens) may have experienced elevated bending forces along the lower limb during walking compared to those with relatively shorter limbs (e.g. the Neandertals). These increased forces could have led to greater reinforcement of joints and diaphyses. These results must be considered when formulating explanations for variation in limb morphology among Pleistocene hominins.

Robusticity and sexual dimorphism in the postcranium of modern hunter-gatherers from Australia

Throughout much of prehistory, humans practiced a hunting and gathering subsistence strategy. Elevated postcranial robusticity and sexually dimorphic mobility patterns are presumed consequences of this strategy, in which males are attributed greater robusticity and mobility than females. Much of the basis for these trends originates from populations where skeletal correlates of activity patterns are known (e.g., cross-sectional geometric properties of long bones), but in which activity patterns are inferred using evidence such as archaeological records (e.g., Pleistocene Europe). Australian hunter-gatherers provide an opportunity to critically assess these ideas since ethnographic documentation of their activity patterns is available. We address the following questions: do skeletal indicators of Australian hunter-gatherers express elevated postcranial robusticity and sexually dimorphic mobility relative to populations from similar latitudes, and do ethnographic accounts support these findings. Using computed tomography, cross-sectional images were obtained from 149 skeletal elements including humeri, radii, ulnae, femora, and tibiae. Cross-sectional geometric properties were calculated from image data and standardized for body size. Australian hunter-gatherers often have reduced robusticity at femoral and humeral midshafts relative to forager (Khoi-San), agricultural/industrialized (Zulu), and industrialized (African American) groups. Australian hunter-gatherers display more sexual dimorphism in upper limb robusticity than lower limb robusticity. Attributing specific behavioral causes to upper limb sexual dimorphism is premature, although ethnographic accounts support sex-specific differences in tool use. Virtually absent sexual dimorphism in lower limb robusticity is consistent with ethnographic accounts of equivalently high mobility among females and males. Thus, elevated postcranial robusticity and sexually dimorphic mobility do not always characterize hunter-gatherers.

Regional variation in the postcranial robusticity of late Upper Paleolithic humans

Early modern humans from the European Upper Paleolithic (UP) demonstrate trends in postcranial biomechanical features that coincide with the last glacial maximum (LGM). These features have been interpreted as evidence that ecological changes of the LGM played a critical role in cultural and biological adaptation in European UP populations. In areas outside of Europe, similar environmental changes occurred with the LGM. This analysis introduces postcranial material from the Late Upper Paleolithic (LUP) of North Africa and Southeast Asia and tests two related hypotheses: 1) LUP samples across the Old World had similar patterns of postcranial robusticity and 2) relative to an available Early Upper Paleolithic (EUP) sample, regional LUP samples demonstrate similar trends in robusticity that may be attributable to climatic effects of the LGM. Cross-sectional geometric data of the humeri and femora were obtained for 26 EUP and 100 LUP humans from Europe, Africa, and Asia. Despite regional differences, LUP samples are similar relative to the EUP sample. In the humerus, bilateral asymmetry decreases in all LUP samples relative to the EUP sample. In the femur, LUP samples demonstrate increasingly circular femoral midshaft sections, reflecting reduced anteroposterior bending strength relative to the EUP sample. These patterns suggest changes in subsistence behavior and mobility after the LGM across the Old World that are most consistent with reduced mobility and broad-spectrum resource exploitation.

In vivo bone strain and bone functional adaptation

Mechanistic interpretations of bone cross-sectional shapes are based on the paradigm of shape optimization such that bone offers maximum mechanical resistance with a minimum of material. Recent in vivo strain studies (Demes et al., Am J Phys Anthropol 106 (1998) 87-100, Am J Phys Anthropol 116 (2001) 257-265; Lieberman et al., Am J Phys Anthropol 123 (2004) 156-171) have questioned these interpretations by demonstrating that long bones diaphyses are not necessarily bent in planes in which they offer maximum resistance to bending. Potential limitations of these in vivo studies have been pointed out by Ruff et al. (Am J Phys Anthropol 129 (2006) 484-498). It is demonstrated here that two loading scenarios, asymmetric bending and buckling, would indeed not lead to correct predictions of loads from strain. It is also shown that buckling is of limited relevance for many primate long bones. This challenges a widely held view that circular bone cross sections make loading directions unpredictable for bones which is based on a buckling load model. Asymmetric bending is a potentially confounding factor for bones with directional differences in principal area moments (I(max) > I(min)). Mathematical corrections are available and should be applied to determine the bending axis in such cases. It is concluded that loads can be reliably extrapolated from strains. More strain studies are needed to improve our understanding of the relationships between activities, bone loading regimes associated with them, and the cross-sectional geometry of bones.

Femur length, body mass, and stature estimates of Orrorin tugenensis, a 6 Ma hominid from Kenya

To understand the palaeobiology of extinct hominids it is useful to estimate their body mass and stature. Although many species of early hominid are poorly preserved, it is occasionally possible to calculate these characteristics by comparison with different extant groups, by use of regression analysis. Calculated body masses and stature determined using these models can then be compared. This approach has been applied to 6 Ma hominid femoral remains from the Tugen Hills, Kenya, attributed to Orrorin tugenensis. It is suggested that the best-preserved young adult individual probably weighed approximately 35-50 kg. Another fragmentary femur results in larger estimates of body mass, indicative of individual variation. The length of the femur of the young adult individual was estimated, by using anthropoid-based regression, to be a minimum of 298 mm. Because whole-femur proportions for Orrorin are unknown, this prediction is conservative and should be revised when additional specimens become available. When this predicted value was used for regression analysis of bonobos and humans it was estimated to be 1.1-1.2 m tall. This value should, however, be viewed as a lower limit.

New Neandertal remains from Cova Negra (Valencia, Spain)

New Neandertal fossils from the Mousterian site of Cova Negra in the Valencia region of Spain are described, and a comprehensive study of the entire human fossil sample is provided. The new specimens significantly augment the sample of human remains from this site and make Cova Negra one of the richest human paleontological sites on the Iberian Peninsula. The new specimens include cranial and postcranial elements from immature individuals and provide an opportunity to study the ontogenetic appearance of adult Neandertal characteristics in this Pleistocene population. Children younger than 10 years of age constitute four of the seven minimum number of individuals in the sample, and this relative abundance of children at Cova Negra is similar that in to other Neandertal sites in Europe and southwest Asia. The recognition of diagnostic Neandertal features in several of the specimens, as well as their western European context and late Pleistocene age, suggests that all the human remains from Cova Negra represent Neandertals. The archaeological evidence from Cova Negra indicates sporadic, short-term occupations of the site, suggesting a high degree of mobility among Neandertals.

A fossil hominoid proximal femur from Kikorongo Crater, southwestern Uganda

The external morphology of a fragmentary right proximal femur from southwestern Uganda is described here. Discovered in the Kikorongo Crater of Queen Elizabeth National Park in 1961, this specimen was informally assigned to Homo sapiens (although never described) and tentatively dated to the late Pleistocene. However, because aspects of the external morphology of the femur align the fossil with the African great apes, we suggest that the Kikorongo femur may be the first postcranial fossil of the genus Pan. Like the African apes, the Kikorongo specimen lacks both an obturator externus groove and an intertrochanteric line. It has a short femoral neck with a circular cross section, and a narrow and deep superior notch. Using resampling statistics and discriminant function analysis, the Kikorongo femur clustered with the genus Pan, as opposed to Gorilla or Homo. However, if the specimen is from Pan, it would be large for this taxon. Furthermore, features that clearly distinguish the external morphology of Plio-Pleistocene hominin proximal femora from African ape femora, such as the shape of the femoral neck in cross section and femoral neck length, have converged in Holocene humans and African apes. Unfortunately, the internal morphology of the femoral neck of the Kikorongo fossil was not discernable. Although we hypothesize that the Kikorongo femur is from the genus Pan, there is such variability in the proximal femora of modern humans that, although it would be an unusual human, it remains possible that this fossil represents H. sapiens.

Body size, body proportions, and mobility in the Tyrolean "Iceman"

Body mass and structural properties of the femoral and tibial midshafts of the "Iceman," a late Neolithic (5,200 BP) mummy found in the Tyrolean Alps, are determined from computed tomographic scans of his body, and compared with those of a sample of 139 males spanning the European early Upper Paleolithic through the Bronze Age. Two methods, based on femoral head breadth and estimated stature/bi-iliac (pelvic) breath, yield identical body-mass estimates of 61 kg for the Iceman. In combination with his estimated stature of 158 cm, this indicates a short but relatively wide or stocky body compared to our total sample. His femur is about average in strength compared to our late Neolithic (Eneolithic) males, but his tibia is well above average. His femur also shows adaptations for his relatively broad body (mediolateral strengthening), while his tibia shows adaptations for high mobility over rough terrain (anteroposterior strengthening). In many respects, his tibia more closely resembles those of European Mesolithic rather than Neolithic males, which may reflect a more mobile lifestyle than was characteristic of most Neolithic males, perhaps related to a pastoral subsistence strategy. There are indications that mobility in general declined between the European Mesolithic and late Neolithic, and that body size and shape may have become more variable throughout the continent following the Upper Paleolithic.

Body size, body proportions, and encephalization in a Middle Pleistocene archaic human from northern China

The unusual discovery of associated cranial and postcranial elements from a single Middle Pleistocene fossil human allows us to calculate body proportions and relative cranial capacity (encephalization quotient) for that individual rather than rely on estimates based on sample means from unassociated specimens. The individual analyzed here (Jinniushan) from northeastern China at 260,000 years ago is the largest female specimen yet known in the human fossil record and has body proportions (body height relative to body breadth and relative limb length) typical of cold-adapted populations elsewhere in the world. Her encephalization quotient of 4.15 is similar to estimates for late Middle Pleistocene humans that are based on mean body size and mean brain size from unassociated specimens.

Body proportions in ancient Andeans from high and low altitudes

Living human populations from high altitudes in the Andes exhibit relatively short limbs compared with neighboring groups from lower elevations as adaptations to cold climates characteristic of high-altitude environments. This study compares relative limb lengths and proportions in pre-Contact human skeletons from different altitudes to test whether ecogeographic variation also existed in Andean prehistory. Maximum lengths of the humerus, radius, femur, and tibia, and femoral head breadth are measured in sex-specific groups of adult human skeletons (N = 346) from the central (n = 80) and the south-central (n = 123) Andean coasts, the Atacama Desert at 2,500 m (n = 102), and the southern Peruvian highlands at 2,000-3,800 m (n = 41). To test whether limb lengths vary with altitude, comparisons are made of intralimb proportions, limb lengths against body mass estimates derived from published equations, limb lengths against the geometric mean of all measurements, and principal component analysis. Intralimb proportions do not statistically differ between coastal groups and those from the Atacama Desert, whereas intralimb proportions are significantly shorter in the Peruvian highland sample. Overall body size and limb lengths relative to body size vary along an altitudinal gradient, with larger individuals from coastal environments and smaller individuals with relatively longer limbs for their size from higher elevations. Ecogeographic variation in relation to climate explains the variation in intralimb proportions, and dietary variation may explain the altitudinal cline in body size and limb lengths relative to body size. The potential effects of gene flow on variation in body proportions in Andean prehistory are also explored.

Body mass prediction from stature and bi-iliac breadth in two high latitude populations, with application to earlier higher latitude humans

Previous studies have indicated that body mass can be estimated from stature and bi-iliac (maximum pelvic) breadth with reasonable accuracy in modern humans, supporting the use of this method to estimate body mass in earlier human skeletal samples. However, to date the method has not been tested specifically on high latitude individuals, whose body form in some ways more closely approximates that of earlier higher latitude humans (i.e., large and broad-bodied). In this study, anthropometric data for 67 Alaskan Inupiat and 54 Finnish adults were used to test the stature/bi-iliac body mass estimation method. Both samples are very broad-bodied, and the Finnish sample is very tall as well. The method generally works well in these individuals, with average directional biases in body mass estimates of 3% or less, except in male Finns, whose body masses are systematically underestimated by an average of almost 9%. A majority of individuals in the total pooled sample have estimates to within +/-10% of their true body masses, and more than three-quarters have estimates to within +/-15%. The major factor found to affect directional bias is shoulder to hip breadth (biacromial/bi-iliac breadth). Male Finns have particularly wide shoulders, which may in part explain their systematic underestimation. New body mass estimation equations are developed that include the new data from this study. When applied to a sample of earlier (late middle Pleistocene to early Upper Paleolithic) higher latitude skeletal specimens, differences between previous and new body estimates are small (less than 2%). However, because the Finns significantly extend the range of morphological variation beyond that represented in the original world-wide reference sample used in developing the method, thereby increasing its generality, it is recommended that these new formulas be used in subsequent body mass estimations.

Estimation of body size and physique from hominin skeletal remains

Three methods of measuring stature from skeletal remains are reviewed: the reconstructed skeletal length, the correspondence of long bone length to stature and the regression of stature on long bone length. Each involves problems and difficulties. For the anthropologist, there is the additional problem of applying findings from extant taxa to extinct taxa with potentially different morphologies and limb proportions. Of the various studies involving regression of the stature the findings of Trotter and Gleser are judged the most robust and useful notwithstanding problems and limitations. The lumbar vertebrae are potentially important as stature predictors. Estimation of body mass from the skeleton is also beset with problems. Eight methods are reviewed: Hartwig-Scherer's taxon independent solution, four methods involving measurements from the weight-bearing appendicular skeleton, Ruff's method using the length of the reconstructed skeleton and an estimate of body breadth, estimates from the total skeletal mass and estimates from the body mass index when the stature is known approximately. Lumbar vertebrae provide reasonable estimates of both body mass and stature and thus by derivation the body mass index. At present both forensic scientists and anthropologists lack adequate data and methods to estimate body size and shape from hominin skeletons. A further large and well-designed study using magnetic resonance imaging is required.

The Maka femur and its bearing on the antiquity of human walking: applying contemporary concepts of morphogenesis to the human fossil record

MAK-VP-1/1, a proximal femur recovered from the Maka Sands (ca. 3.4 mya) of the Middle Awash, Ethiopia, and attributed to Australopithecus afarensis, is described in detail. It represents the oldest skeletal evidence of locomotion in this species, and is analyzed from a morphogenetic perspective. X-ray, CT, and metric data are evaluated, using a variety of methods including discriminant function. The specimen indicates that the hip joint of A. afarensis was remarkably like that of modern humans, and that the dramatic muscle allocation shifts which distinguish living humans and African apes were already present in a highly derived form in this species. Its anatomy provides no indication of any form of locomotion save habitual terrestrial bipedality, which very probably differed only trivially from that of modern humans.

Estimation of torsional rigidity in primate long bones

Comparative studies of long bone biomechanics in primates frequently use the polar moment of inertia (J ) as a variable reflecting overall mechanical rigidity, average bending rigidity, or resistance to torsional shear stresses. While the use of this variable for characterizing the first two properties is appropriate, it is potentially a highly misleading measure of torsional resistance. Errors result from violations of assumptions required for the use of the polar moment of inertia; in particular, the predictive utility of J diminishes with departures from axial symmetry (i.e., a cylindrical cross-sectional shape). The magnitude of these errors is estimated both theoretically and experimentally. It is argued that the use of the polar moment of inertia for estimating long bone torsional rigidity should be restricted to samples of relatively invariant and/or cylindrical geometry. Alternative measures for torsional resistance are evaluated and reviewed.

Articular area responses to mechanical loading: effects of exercise, age, and skeletal location

How reliable are reconstructions of body mass and joint function based on articular surface areas? While the dynamic relationship between mechanical loading and cross-sectional geometry in long bones is well-established, the effect of loading on the subchondral articular surface area of epiphyses (hereafter, articular surface area, or ASA) has not been experimentally tested. The degree to which ASA can change in size and shape is important, because articular dimensions are frequently used to estimate body mass and positional behavior in fossil species. This study tests the hypothesis that mechanical loading influences ASA by comparing epiphyses of exercised and sedentary sheep from three age categories: juvenile, subadult, and adult (n = 44). ASA was measured on latex molds of subchondral articular surfaces of 10 epiphyses from each sheep. Areas were standardized by body mass, and compared to diaphyseal cross-sectional geometrical data. Nonparametric statistical comparisons of exercised and control individuals found no increases in ASA in response to mechanical loading in any age group. In contrast, significant differences in diaphyseal cross-sectional geometry were detected between exercised and control groups, but mostly in juveniles. The conservatism of ASA supports the hypothesis that ASA is ontogenetically constrained, and related to locomotor behavior at the species level and to body mass at the individual level, while variations in diaphyseal cross-sectional geometry are more appropriate proxies for individual variations in activity level.

Recently identified postcranial remains of Paranthropus and early Homo from Swartkrans Cave, South Africa

Fifteen newly recognized hominid postcranials from Swartkrans are described here and compared with a sample of previously described early hominids, African apes and modern humans. Ten of the new specimens are from Member 1. Two are from Member 2 and three are from Member 3. Nine of the fossils are referred to Paranthropus, three to Homo, and three specimens cannot be assigned at present. The collection of hominid postcranials from Members 1-3 at Swartkrans now numbers more than 70 specimens. With the description of two new, small femoral heads, SKW 19 and SK 3121, there are now four proximal femora from Swartkrans. When SK 82 and SK 97 are compared with SKW 19 and SK 3121, the two sets offer important insights into body size and sexual dimorphism in Paranthropus robustus.A new distal femur, SK 1896 and other bones attributed to Homo cf. erectus, indicate that male Homo were larger than Paranthropus at Swartkrans.

The revolution that wasn't: a new interpretation of the origin of modern human behavior

Proponents of the model known as the "human revolution" claim that modern human behaviors arose suddenly, and nearly simultaneously, throughout the Old World ca. 40-50 ka. This fundamental behavioral shift is purported to signal a cognitive advance, a possible reorganization of the brain, and the origin of language. Because the earliest modern human fossils, Homo sapiens sensu stricto, are found in Africa and the adjacent region of the Levant at >100 ka, the "human revolution" model creates a time lag between the appearance of anatomical modernity and perceived behavioral modernity, and creates the impression that the earliest modern Africans were behaviorally primitive. This view of events stems from a profound Eurocentric bias and a failure to appreciate the depth and breadth of the African archaeological record. In fact, many of the components of the "human revolution" claimed to appear at 40-50 ka are found in the African Middle Stone Age tens of thousands of years earlier. These features include blade and microlithic technology, bone tools, increased geographic range, specialized hunting, the use of aquatic resources, long distance trade, systematic processing and use of pigment, and art and decoration. These items do not occur suddenly together as predicted by the "human revolution" model, but at sites that are widely separated in space and time. This suggests a gradual assembling of the package of modern human behaviors in Africa, and its later export to other regions of the Old World. The African Middle and early Late Pleistocene hominid fossil record is fairly continuous and in it can be recognized a number of probably distinct species that provide plausible ancestors for H. sapiens. The appearance of Middle Stone Age technology and the first signs of modern behavior coincide with the appearance of fossils that have been attributed to H. helmei, suggesting the behavior of H. helmei is distinct from that of earlier hominid species and quite similar to that of modern people. If on anatomical and behavioral grounds H. helmei is sunk into H. sapiens, the origin of our species is linked with the appearance of Middle Stone Age technology at 250-300 ka.

Neandertal knees: power lifters in the Pleistocene?

It has been proposed (Trinkaus, 1983 a; Miller & Gross, 1998) that the marked thickness of Neandertal patellae and/or the posterior displacement of their tibial condyles increased their relative M. quadriceps femoris moment arms, thereby making their legs powerful in extension. However, it is necessary to compare these reflections of muscle moment arm length to appropriate measures of the body weight moment arm and body mass estimates, both of which are influenced by ecogeographically determined body proportions. Reassessment of tibial condylar displacement and patellar thickness, as well as patellar height, relative to an appropriate measure of the moment arm for the baseline load on the knee (body weight), to that moment arm times estimated body mass, and to that moment arm times a skeletal reflection of body mass (femoral head diameter) rejects the hypothesis that the Neandertals had exceptionally powerful knee extension. Relative tibial condylar displacement remains above that of a modern industrial society sample, but similar to that of the Broken Hill tibia, Late Pleistocene early modern humans and a recent human nonindustrial sample. Relative patellar thickness is similar to that of early modern humans, who have relatively thick patellae compared to the late Holocene human samples. Consequently, once body proportions are taken into account, there is little difference between the Neandertals and other later Pleistocene humans in knee extensor mechanical advantage, and all of these fossil hominids are similar in the more important proximal tibial proportions to those of nonindustrial recent humans.

The anomalous archaic Homo femur from Berg Aukas, Namibia: a biomechanical assessment

The probably Middle Pleistocene human femur from Berg Aukas, Namibia, when oriented anatomically and analyzed biomechanically, presents an unusual combination of morphological features compared to other Pleistocene Homo femora. Its midshaft diaphyseal shape is similar to most other archaic Homo, but its subtrochanteric shape aligns it most closely with earlier equatorial Homo femora. It has an unusually low neck shaft angle. Its relative femoral head size is matched only by Neandertals with stocky hyperarctic body proportions. Its diaphyseal robusticity is modest for a Neandertal, but reasonable compared to equatorial archaic Homo femora. Its gluteal tuberosity is relatively small. Given its derivation from a warm climatic region, it is best interpreted as having had relatively linear body proportions (affecting proximal diaphyseal proportions, shaft robusticity, and gluteal tuberosity size) combined with an elevated level of lower limb loading during development (affecting femoral head size and neck shaft angle).

The Middle Pleistocene human tibia from Boxgrove

The Boxgrove tibia was discovered in 1993, associated with Middle Pleistocene fauna, and Lower Palaeolithic archaeology. The sediments at Boxgrove were deposited during a temperate interglacial episode and ensuing cold stage. They thus represent a wide range of modes and environments of deposition. Archaeological remains have been excavated from all the major stratigraphic units, giving a continuity of occupation for this part of southern England over a 10(4) year timescale, through markedly changing climatic regimes. The stratigraphic, archaeological and sedimentological contexts of the tibia are described, as well as its preservation and morphology. Measurements are given, with discussion of reconstructed bone length, and stature estimates. Comparative measurements are provided for fossil and recent human samples: the large dimensions of its diaphysis place the Boxgrove tibia near or beyond the upper size limits of the comparative samples, but its reconstructed length and estimated stature are less exceptional. The elevated robusticity of the specimen indicates exceptional diaphyseal strength and/or cold adapted body proportions paralleling those of the Neanderthals. Disagreement about the taxonomy of Middle Pleistocene hominids and lack of comparable fossil material make a specific assignment for the Boxgrove tibia problematic. The tibia can only definitely be assigned to non-modern Homo sp., with possible further reference to Homo cf. heidelbergensis (Schoetensack, 1908) on temporal and geographic grounds, if the validity of that species is accepted.

Appendicular robusticity and the paleobiology of modern human emergence

The emergence of modern humans in the Late Pleistocene, whatever its phylogenetic history, was characterized by a series of behaviorally important shifts reflected in aspects of human hard tissue biology and the archeological record. To elucidate these shifts further, diaphyseal cross-sectional morphology was analyzed by using cross-sectional areas and second moments of area of the mid-distal humerus and midshaft femur. The humeral diaphysis indicates a gradual reduction in habitual load levels from Eurasian late archaic, to Early Upper Paleolithic early modern, to Middle Upper Paleolithic early modern hominids, with the Levantine Middle Paleolithic early modern humans being a gracile anomalous outlier. The femoral diaphysis, once variation in ecogeographically patterned body proportions is taken into account, indicates no changes across the pre-30,000 years B.P. samples in habitual locomotor load levels, followed by a modest decrease through the Middle Upper Paleolithic.

Technical note: CT determination of the mineral density of dry bone specimens using the dipotassium phosphate phantom

Recent studies have demonstrated the potential application of computed tomography (CT) in research into bone density. Clinical studies of bone density using CT commonly employ a dipotassium phosphate phantom to calibrate measurements of mineral density. Designed for in vivo studies, the use of this phantom requires that bones be scanned while immersed in and permeated by fluids or soft tissues similar to water in X-ray attenuation coefficient. However, this condition may not always be met in anthropological applications, which often involve rare and fragile specimens. This study compares mineral density values calculated for a sample of bones scanned-at the same sites-in air and in water. The results indicate that, when scanned in air, the mineral density of trabecular bone is dramatically underestimated, while that of cortical bone is slightly overestimated. We present a linear regression equation to correct this error but recommend that, when possible, researchers calculate their own regressions based on their specific scanning conditions.

Re-analysis of the hominid radii from Cave of Hearths and Klasies River Mouth, South Africa

Two of the few postcranial fragments from the late Early Stone Age and/or the Middle Stone Age of southern Africa are the proximal radii from the Cave of Hearths and Klasies River Mouth. The Cave of Hearths fossil is metrically indistinguishable from both archaic (e.g., Neandertals) and recent humans, and presents a mosaic of primitive and modern features. The primitive include a relatively slender neck and thick cortical bone (the latter of which distinguishes recent humans from archaic, Early Modern, and Upper Paleolithic hominids); the modern includes an anteromedially (rather than medially) facing radial tuberosity. Its extreme collo-diaphyseal angle is unusual, although it can be matched by modern homologues. The neck-shaft angle of some Neandetral and Early Modern radii also appears to match that of the Cave of Hearths specimen. The Klasies River Mouth radius also has thick cortical bone of the neck. It is morphologically indistinguishable from Early Modern and Neandertal homologues. These, and other fossils, suggest a mosaic pattern of evolution in the postcranial skeleton of the late Early Stone Age and/or Middle Stone Age inhabitants of sub-Saharan Africa.