Skeletal growth and function in the California gull (Larus californicus)

Although the bones of rapidly growing animals are composed of weak tissue, they often must function in locomotor activity. We address the conflict between development and skeletal function by analysing the ontogeny of skeletal strength in the California gull, Larus californicus. Changes in shape and mechanical properties of the femur, tibia, tarsometatarsus, humerus, ulna and carpometacarpus were analysed in a complete post-hatching growth series. During post-hatching growth, strength and stiffness of the skeletal tissue increases six- to ten-fold. At hatching, long bones of the wing are relatively weak and they remain so throughout the major portion of the growth period. However, in the hind limb, relatively thick bones in juveniles compensate for the weak tissue such that the force required to break the bones remains constant relative to body mass. This difference between hind limb and wing parallels the development of locomotor function; young gulls begin to walk within a day or two of hatching, but they do not fly until they are fully grown. Thus, in the bones of the hind limb, the conflict between rapid growth and skeletal function is solved by negative allometry of bone thickness.
After young gulls reach adult size, the breaking strength of the wing bones increases three- to four-fold, the mass of the pectoralis muscle triples and the surface area of the wing doubles. The one aspect of wing development that is not delayed until shortly before fledging is linear growth of the bones. Bones of the wing increase in length at a rapid and relatively constant rate from the time of hatching to the attainment of adult size. Relatively early initiation of linear growth of the wing bones suggests that the rate at which bones grow in length may be the rate limiting factor in wing development.     

柳江人身体大小和形状——体重、身体比例及相对脑量的分析

发现于广西柳江的更新世晚期人类化石除1具完整的头骨外,还包含有右侧髋骨、骶骨、两段股骨及若干件椎骨。根据各方面的特征分析,初步认定这些化石属于同一个体。这一有利条件为我们比较准确地获取与该个体身体大小和形状有关的指标数据提供了可能。本文通过对柳江人头骨及复原骨盆的测量,计算了柳江人的身高、体重、身体比例、相对脑量等。在此基础上分析了柳江人的身体大小和形状。本研究发现:柳江人化石所代表的个体具有适应温暖气候环境的纤细型身体比例,代表相对脑量的EQ指数5.602大于金牛山、山顶洞等中国更新世中、晚期化石人类,而与包括港川人在内的更新世末期及现代人类的EQ指数接近。柳江人体重52.0kg小于金牛山、山顶洞、尼安德特人等生活在高纬度地区的化石人类,而与港川、非洲的KNM-ER3883、KNM-ER3733等生活在温暖环境的古人类接近。作者认为这些发现除说明柳江人生活的气候环境外,还提示柳江人身体大小、比例及相对脑量与更新世末期及现代人类接近。     

Intrapopulation variation in stature and body proportions: social status and sex differences in an Italian medieval population (Trino Vercellese, VC)

The phenotypic expression of adult body size and shape results from synergistic interactions between hereditary factors and environmental conditions experienced during growth. Variation in body size and shape occurs even in genetically relatively homogeneous groups, due to different occurrence, duration, and timing of growth insults. Understanding the causes and patterns of intrapopulation variation can foster meaningful information on early life conditions in living and past populations. This study assesses the pattern of biological variation in body size and shape attributable to sex and social status in a medieval Italian population. The sample includes 52 (20 female, 32 male) adult individuals from the medieval population of Trino Vercellese, Italy. Differences in element size and overall body size (skeletal height and body mass) were assessed through Monte Carlo methods, while univariate non-parametric tests and Principal Component Analysis (PCA) were employed to examine segmental and overall body proportions. Discriminant Analysis was employed to determine the predictive value of individual skeletal elements for social status in the population. Our results highlight a distinct pattern in body size and shape variation in relation to status and sex. Male subsamples exhibit significant postcranial variation in body size, while female subsamples express smaller, nonsignificant differences. The analysis of segmental proportions highlighted differences in trunk/lower limb proportions between different status samples, and PCA indicated that in terms of purely morphological variation high status males were distinct from all other groups. The pattern observed likely resulted from a combination of biological factors and cultural practices.     

Body size, body shape, and long bone strength in modern humans

To identify behaviorally significant differences in bone structure it is first necessary to control for the effects of body size and body shape. Here the scaling of cross-sectional geometric properties of long bone diaphyses with different "size" measures (bone length, body mass, and the product of bone length and body mass) are compared in two modern human populations with very different body proportions: Pecos Pueblo Amerindians and East Africans. All five major long bones (excluding the fibula) were examined. Mechanical predictions are that cortical area (axial strength) should scale with body mass, while section modulus (bending/torsional strength) should scale with the product of body mass and moment arm length. These predictions are borne out for section moduli, when moment arm length is taken to be proportional to bone length, except in the proximal femoral diaphysis, where moment arm length is proportional to mediolateral body breadth (as would be expected given the predominance of M-L bending loads in this region). Mechanical scaling of long bone bending/torsional strength is similar in the upper and lower limbs despite the fact that the upper limb is not weight-bearing. Results for cortical area are more variable, possibly due to a less direct dependence on mechanical factors. Use of unadjusted bone length alone as a "size" measure produces misleading results when body shape varies significantly, as is the case between many modern and fossil hominid samples. In such cases a correction factor for body shape should be incorporated into any "size" standardization.     

Bony pelvic canal size and shape in relation to body proportionality in humans

Obstetric selection acts on the female pelvic canal to accommodate the human neonate and contributes to pelvic sexual dimorphism. There is a complex relationship between selection for obstetric sufficiency and for overall body size in humans. The relationship between selective pressures may differ among populations of different body sizes and proportions, as pelvic canal dimensions vary among populations. Size and shape of the pelvic canal in relation to body size and shape were examined using nine skeletal samples (total female n = 57; male n = 84) from diverse geographical regions. Pelvic, vertebral, and lower limb bone measurements were collected. Principal component analyses demonstrate pelvic canal size and shape differences among the samples. Male multivariate variance in pelvic shape is greater than female variance for North and South Africans. High‐latitude samples have larger and broader bodies, and pelvic canals of larger size and, among females, relatively broader medio‐lateral dimensions relative to low‐latitude samples, which tend to display relatively expanded inlet antero‐posterior (A‐P) and posterior canal dimensions. Differences in canal shape exist among samples that are not associated with latitude or body size, suggesting independence of some canal shape characteristics from body size and shape. The South Africans are distinctive with very narrow bodies and small pelvic inlets relative to an elongated lower canal in A‐P and posterior lengths. Variation in pelvic canal geometry among populations is consistent with a high degree of evolvability in the human pelvis. Am J Phys Anthropol 151:88–101, 2013. © 2013 Wiley Periodicals, Inc.     

Habitual throwing and swimming correspond with upper limb diaphyseal strength and shape in modern human athletes

Variation in upper limb long bone cross‐sectional properties may reflect a phenotypically plastic response to habitual loading patterns. Structural differences between limb bones have often been used to infer past behavior from hominin remains; however, few studies have examined direct relationships between behavioral differences and bone structure in humans. To help address this, cross‐sectional images (50% length) of the humeri and ulnae of university varsity‐level swimmers, cricketers, and controls were captured using peripheral quantitative computed tomography. High levels of humeral robusticity were found in the dominant arms of cricketers, and bilaterally among swimmers, whereas the most gracile humeri were found in both arms of controls, and the nondominant arms of cricketers. In addition, the dominant humeri of cricketers were more circular than controls. The highest levels of ulnar robusticity were also found in the dominant arm of cricketers, and bilaterally amongst swimmers. Bilateral asymmetry in humeral rigidity among cricketers was greater than swimmers and controls, while asymmetry for ulnar rigidity was greater in cricketers than controls. The results suggest that more mechanically loaded upper limb elements––unilaterally or bilaterally––are strengthened relative to less mechanically loaded elements, and that differences in mechanical loading may have a more significant effect on proximal compared to distal limb segments. The more circular humerus in the dominant arm in cricketers may be an adaptation to torsional strain associated with throwing activities. The reported correspondence between habitual activity patterns and upper limb diaphyseal properties may inform future behavioral interpretations involving hominin skeletal remains. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Human body mass estimation: a comparison of "morphometric" and "mechanical" methods

In the past, body mass was reconstructed from hominin skeletal remains using both "mechanical" methods which rely on the support of body mass by weight-bearing skeletal elements, and "morphometric" methods which reconstruct body mass through direct assessment of body size and shape. A previous comparison of two such techniques, using femoral head breadth (mechanical) and stature and bi-iliac breadth (morphometric), indicated a good general correspondence between them (Ruff et al. [1997] Nature 387:173-176). However, the two techniques were never systematically compared across a large group of modern humans of diverse body form. This study incorporates skeletal measures taken from 1,173 Holocene adult individuals, representing diverse geographic origins, body sizes, and body shapes. Femoral head breadth, bi-iliac breadth (after pelvic rearticulation), and long bone lengths were measured on each individual. Statures were estimated from long bone lengths using appropriate reference samples. Body masses were calculated using three available femoral head breadth (FH) formulae and the stature/bi-iliac breadth (STBIB) formula, and compared. All methods yielded similar results. Correlations between FH estimates and STBIB estimates are 0.74-0.81. Slight differences in results between the three FH estimates can be attributed to sampling differences in the original reference samples, and in particular, the body-size ranges included in those samples. There is no evidence for systematic differences in results due to differences in body proportions. Since the STBIB method was validated on other samples, and the FH methods produced similar estimates, this argues that either may be applied to skeletal remains with some confidence.     

Size, structure and gender: lessons about fracture risk

The differences in age-related fracture risks among men and women must reflect gender differences in the relevant variables. We are concerned here with gender differences in structural variables that relate to the size and shape of bones. As children grow, their bones grow in diameter through periosteal modeling. Studies show that radial growth is driven by mechanical forces and is not just "genetically programmed". Moving bone mass farther from the center of the diaphysis makes it more effective in resisting bending and twisting forces, and disproportionately so in comparison to changes in bone mass. Gender differences in long bone structure appear to arise because the bone cells of males and females function in different hormonal environments which affect their responses to mechanical loading. In girls, bone formation on the metacarpal periosteal surface essentially stops at puberty, and is replaced by formation on the endosteal surface, reducing endosteal diameter until about age 20. Bone strength is 60% greater in male metacarpals than in those of females because bone is added periosteally in boys and endosteally in girls. At menopause endosteal resorption resumes, accompanied by slow periosteal apposition, weakening cortical structure. Similar phenomena occur in such critical regions as the femoral neck. Another fundamental gender difference in skeletal development is that whole body bone mineral content increases in linear proportion to lean body mass throughout skeletal maturation in boys, but in girls there is a distinct increase in the slope of this relationship at puberty, when estrogen rises. Frost's hypothesis is that this reflects an effect of estrogen on bone's mechanostat set point, and this is increasingly supported by data showing that estrogen and mechanical strain act through a common pathway in osteoblast-like cells. If Frost's hypothesis is correct, the mechanostat is set for maximal effect of mechanical loading on bone gain during the 2-3 years preceding menarche. During the childbearing years, the set point is at an intermediate level, and at menopause, it shifts again to place the skeleton into the metabolic equivalent of a disuse state. The most direct approach to resolving this problem would be to simulate the putative effect of estrogen on the set point itself.     

Body weight prediction in early fossil hominids: Towards a taxon-“independent” approach

The choice of a model taxon is crucial when investigating fossil hominids that clearly do not resemble any extant species (such as Australopithecus) or show significant differences from modern human proportions (such as Homo habilis OH 62). An “interhominoid” combination is not adequate either, as scaling with body weight is strongly divergent in African apes and humans for most skeletal predictors investigated here. Therefore, in relation to a study of seven long bone dimensions, a new taxon-“independent” approach is suggested. For a given predictor, its taxonomic “independence” is restricted to the size range over which the body weight-predictor relationship for African apes and humans converges. Different predictors produce converging body weight estimates (BWEs) for different size ranges: taxon-“independent” estimates can be calculated for small- and medium-sized hominids (e. g., for weights below 50 kg) using femoral and tibial dimensions, whereas upper limb bones provide converging results for large hominids (above 50 kg). If the remains of Australopithecus afarensis really belong to one species, the relationship of male (above 60 kg) to female body weight (approximately 30 kg) does not fall within the observed range of modern hominoids. Considering Sts 14 (22 kg) to represent a small-sized Australopithecus africanus, the level of encephalization lies well above that of extant apes. If OH 62 (approximately 25 kg), with limb proportions less human-like than those of australopithecines, indeed represents Homo habilis (which has been questioned previously), an increase in relative brain size would have occurred well before full bipedality, an assumption running counter to current assumptions concerning early human evolution. © 1993 Wiley-Liss, Inc.     

Patterns of joint size dimorphism in the elbow and knee of catarrhine primates

Differences in body size between conspecific sexes may incur differences in the relative size and/or shape of load-bearing joints, potentially confounding our understanding of variation in the fossil record. More specifically, larger males may experience relatively greater limb joint stress levels than females, unless an increase in weight-related forces is compensated for by positive allometry of articular surface areas. This study examines variation in limb joint size dimorphism (JSD) among extant catarrhines to: 1) determine whether taxa exhibit JSD beyond that expected to simply maintain geometric similarity between sexes, and 2) test whether taxa differ in JSD (relative to body size dimorphism) with respect to differences in limb use and/or phylogeny. "Joint size" was quantified for the distal humerus and distal femur of 25 taxa. Analysis of variance was used to test for differences between sexes (in joint size ratios) and among taxa (in patterns of dimorphism). Multiple regression was used to examine differences in JSD among taxa after accounting for variation in body size dimorphism (BSD) and body size. Although degrees of humeral and femoral JSD tend to be the same within species, interspecific variation exists in the extent to which both joints are dimorphic relative to BSD. While most cercopithecoids exhibit relatively high degrees of JSD (i.e., positive allometry), nonhuman hominoids exhibit degrees of JSD closer to isometry. These results may reflect a fundamental distinction between cercopithecoids and hominoids in joint design. Overall, the results make more sense (from a mechanical standpoint) when adjustments to BSD are made to account for the larger effective female body mass associated with bearing offspring. In contrast to other hominoids, modern humans exhibit relatively high JSD in both the knee and elbow (despite lack of forelimb use in weight support). Estimates of BSD based on fossil limb bones will vary according to the extant analogue chosen for comparison.     

Predicting body mass of bonobos (Pan paniscus) with human-based morphometric equations

A primate's body mass covaries with numerous ecological, physiological, and behavioral characteristics. This versatility and potential to provide insight into an animal's life has made body mass prediction a frequent and important objective in paleoanthropology. In hominin paleontology, the most commonly employed body mass prediction equations (BMPEs) are “mechanical” and “morphometric”: uni- or multivariate linear regressions incorporating dimensions of load-bearing skeletal elements and stature and living bi-iliac breadth as predictor variables, respectively. The precision and accuracy of BMPEs are contingent on multiple factors, however, one of the most notable and pervasive potential sources of error is extrapolation beyond the limits of the reference sample. In this study, we use a test sample requiring extrapolation—56 bonobos (Pan paniscus) from the Lola ya Bonobo sanctuary in Kinshasa, Democratic Republic of the Congo—to evaluate the predictive accuracy of human-based morphometric BMPEs. We first assess systemic differences in stature and bi-iliac breadth between humans and bonobos. Due to significant differences in the scaling relationships of body mass and stature between bonobos and humans, we use panel regression to generate a novel BMPE based on living bi-iliac breadth. We then compare the predictive accuracy of two previously published morphometric equations with the novel equation and find that the novel equation predicts bonobo body mass most accurately overall (41 of 56 bonobos predicted within 20% of their observed body mass). The novel BMPE is particularly accurate between 25 and 45 kg. Given differences in limb proportions, pelvic morphology, and body tissue composition between the human reference and bonobo test samples, we find these results promising and evaluate the novel BMPE's potential application to fossil hominins.     

Effects of 5 weeks of lower limb suspension on muscle size and strength

Lack of weight-bearing, as occurs in space, appears to be associated with reductions in strength and mass of skeletal muscle. Very limited data, however, is at hand describing changes in skeletal muscle size and function following manned space missions. Our current knowledge therefore is mainly based on studies of space flown rats. It is obvious though that this information, only in part can be extrapolated to humans. A few bed rest studies have demonstrated that decreases in strength and muscle size are substantial. At this time, however, the magnitude or time course of such changes either in response to space flight or simulations of microgravity have not been defined. In the last few years we have employed a human model to simulate unloading of lower limb skeletal muscles that occurs in microgravity. This model was essentially adopted from the rat hindlimb suspension technique. The purpose of this study was to assess the magnitude of decreases in muscle strength and size as a result of five weeks of unilateral lower limb suspension.     

Developmental basis of limb length in rodents: evidence for multiple divisions of labor in mechanisms of endochondral bone growth

SUMMARY Mammals are remarkably diverse in limb lengths and proportions, but the number and kind of developmental mechanisms that contribute to length differences between limb bones remain largely unknown. Intra- and interspecific differences in bone length could result from variations in the cellular processes of endochondral bone growth, creating differences in rates of chondrocyte proliferation or hypertrophy, variation in the shape and size of chondrocytes, differences in the number of chondrocytes in precursor populations and throughout growth, or a combination of these mechanisms. To address these questions, this study compared cellular mechanisms of endochondral bone growth in cross-sectional ontogenetic series of the appendicular skeleton of two rodent species: the mouse ( Mus musculus ) and Mongolian gerbil ( Meriones unguiculatus ). Results indicate that multiple cellular processes of endochondral bone growth contribute to phenotypic differences in limb bone length. The data also suggest that separate developmental processes contribute to intraspecific length differences in proximal versus distal limb bones, and that these proximo-distal mechanisms are distinct from mechanisms that contribute to interspecific differences in limb bone length related to body size. These developmental "divisions of labor" are hypothesized to be important features of vertebrate limb development that allow (1) morphology in the autopods to evolve independently of the proximal limb skeleton, and (2) adaptive changes in limb proportions related to locomotion to evolve independently of evolutionary changes in body size.     

Estimating stature in fossil hominids: which regression model and reference sample to use?

coResearchers have long appreciated the significant relationship between body size and an animal's overall adaptive strategy and life history. However, much more emphasis has been placed on interpreting body size than on the actual calculation of it. One measure of size that is especially important for human evolutionary studies is stature. Despite a long history of investigation, stature estimation remains plagued by two methodological problems: (1) the choice of the statistical estimator, and (2) the choice of the reference population from which to derive the parameters.This work addresses both of these problems in estimating stature for fossil hominids, with special reference to A.L. 288-1 (Australopithecus afarensis) and WT 15000 (Homo erectus). Three reference samples of known stature with maximum humerus and femur lengths are used in this study: a large (n=2209) human sample from North America, a smaller sample of modern human pygmies (n=19) from Africa, and a sample of wild-collected African great apes (n=85). Five regression techniques are used to estimate stature in the fossil hominids using both univariate and multivariate parameters derived from the reference samples: classical calibration, inverse calibration, major axis, reduced major axis and the zero-intercept ratio model. We also explore a new diagnostic to test extrapolation and allometric differences with multivariate data, and we calculate 95% confidence intervals to examine the range of variation in estimates for A.L. 288-1, WT 15000 and the new Bouri hominid (contemporary with [corrected] Australopithecus garhi). Results frequently vary depending on whether the data are univariate or multivariate. Unique limb proportions and fragmented remains complicate the choice of estimator. We are usually left in the end with the classical calibrator as the best choice. It is the maximum likelihood estimator that performs best overall, especially in scenarios where extrapolation occurs away from the mean of the reference sample. The new diagnostic appears to be a quick and efficient way to determine at the outset whether extrapolation exists in size and/or shape of the long bones between the reference sample and the target specimen.     

Geographic variation in body form of prehistoric Jomon males in the Japanese archipelago: Its ecogeographic implications

Diversity of human body size and shape is often biogeographically interpreted in association with climatic conditions. According to Bergmann's and Allen's rules, populations in regions with a cold climate are expected to display an overall larger body and smaller/shorter extremities than those in warm/hot environments. In the present study, the skeletal limb size and proportions of prehistoric Jomon hunter‐gatherers, who extensively inhabited subarctic to subtropical areas in the ancient Japanese archipelago, were examined to evaluate whether or not the inter‐regional differences follow such ecogeographic patterns. Results showed that the Jomon intralimb proportions including relative distal limb lengths did not differ significantly among five regions from northern Hokkaido to the southern Okinawa Islands. This suggests a limited co‐variability of the intralimb proportions with climate, particularly within genealogically close populations. In contrast, femoral head breadth (associated with body mass) and skeletal limb lengths were found to be significantly and positively correlated with latitude, suggesting a north‐south geographical cline in the body size. This gradient therefore comprehensively conforms to Bergmann's rule, and may stem from multiple potential factors such as phylogenetic constraints, microevolutionary adaptation to climatic/geographic conditions during the Jomon period, and nutritional and physiological response during ontogeny. Specifically, the remarkably small‐bodied Jomon in the Okinawa Islands can also be explained as an adjustment to subtropical and insular environments. Thus, the findings obtained in this study indicate that Jomon people, while maintaining fundamental intralimb proportions, displayed body size variation in concert with ambient surroundings. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Ontogeny and limb bone scaling in two new world marsupials,Monodelphis domestica and Didelphis virginiana

This study examines the growth of two species of marsupials who share common ancestry and are born at the same neonatal size of a little less than 1 g. Despite this similarity at birth, adult size of these two species differs by about 50 times, with the smaller species believed to be the more ancestral. We quantified the growth in the limb bones (humerus, femur, ulna, tibia, metacarpal, and metatarsal) beginning around 40 days of age until adult size was reached. Results indicate that the larger species grows at a higher rate of growth as well as for a longer period of time to reach its larger adult size. Despite these differences in growth, there were few differences observed in the scaling over time of length to width in the various limb bones that were measured. The two species, although different in their adult size and the patterns of growth, maintain the same length to width proportions in each limb bone. The biggest difference between species in scaling was observed in the bones of the hands and feet, which may suggest adaptation to size and/or locomotor performance as body size increases. Despite variation in size, these heterochronic patterns do not affect the shape among adults or over evolutionary time. J Morphol 231:117–130, 1997. © 1997 Wiley-Liss, Inc.     

Descriptions of the upper limb skeleton of Homo floresiensis

Several bones of the upper extremity were recovered during excavations of Late Pleistocene deposits at Liang Bua, Flores, and these have been attributed to Homo floresiensis. At present, these upper limb remains have been assigned to six different individuals - LB1, LB2, LB3, LB4, LB5, and LB6. Several of these bones are complete or nearly so, but some are quite fragmentary. All skeletal remains recovered from Liang Bua were extremely fragile, but have now been stabilized and hardened in the laboratory in Jakarta. They are now curated in museum-quality containers at the National Research and Development Centre for Archaeology in Jakarta, Indonesia. These skeletal remains are described and illustrated photographically. The upper limb presents a unique mosaic of derived (human-like) and primitive morphologies, the combination of which is never found in either healthy or pathological modern humans.     

Accumulations osseuses en périphérie de terriers de petits carnivores : les stigmates de prédation et de fréquentation

Faunal remains from spoil heaps of two burrows inhabited by small carnivores (fox and badger) are analysed from a taphonomical point of view. This analysis provides characteristics for bone accumulation produced by small carnivores and will be a powerful tool for deciphering site formation about the occupational alternation of small carnivores and humans. Identified species were grouped by size classes. Faunal spectrum is composed by varied species of microfauna (70%), mesofauna (30%). Macromammal remains are under represented (less than 1%) and come from scavenged carcasses. Predators and consumed species are compared on the basis of the skeletal part representation, age classes and recording of predation marks (gnawed and digested bones). Skeletal part representation shows that all taxons exhibit a low-representation of axial skeleton and autopodial bones. Predators show a high representation of hind limb bones and a low representation of the fore limb bones whereas consumed species exhibit a reverse pattern. Mortality curve analysis provides an attritional profile for carnivores and helps for the establishment of the season of occupation of the burrow. Adults largely dominate consumed species. Moreover, predation marks are found in 1% of the carnivores’ bones and from 15% to more than 40% on prey bones. The large-sized prey bones only wear gnawed marks (20%) and anthropic marks (10–20%) whereas microfaunal remains exhibits more digested marks (40%) than gnawing stigmata (5%). Medium-sized animals bones wear both marks and with the same proportions (10–15%).