The Functional and Allometric Implications of Hipbone Trabecular Microarchitecture in a Sample of Eutherian and Metatherian Mammals (original) (raw)
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American Journal of Physical Anthropology
"Although the correspondence between habitual activity and diaphyseal cortical bone morphology has been demonstrated for the fore- and hind-limb long bones of primates, the relationship between trabecular bone architecture and locomotor behavior is less certain. If sub-articular trabecular and diaphyseal cortical bone morphology reflects locomotor patterns, this correspondence would be a valuable tool with which to interpret morphological variation in the skeletal and fossil record. To assess this relationship, high-resolution computed tomography images from both the humeral and femoral head and midshaft of 112 individuals from eight anthropoid genera (Alouatta, Homo, Macaca, Pan, Papio, Pongo, Trachypithecus, and Symphalangus) were analyzed. Within-bone (subarticular trabeculae vs. mid-diaphysis), between-bone (forelimb vs. hind limb), and among-taxa relative distributions (femoral:humeral) were compared. Three conclusions are evident: (1) Correlations exists between humeral head sub-articular trabecular bone architecture and mid-humerus diaphyseal bone properties; this was not the case in the femur. (2) In contrast to comparisons of inter-limb diaphyseal bone robusticity, among all species femoral head trabecular bone architecture is significantly more substantial (i.e., higher values for mechanically relevant trabecular bone architectural features) than humeral head trabecular bone architecture. (3) Interspecific comparisons of femoral morphology relative to humeral morphology reveal an osteological ‘‘locomotor signal" indicative of differential use of the forelimb and hind limb within mid-diaphysis cortical bone geometry, but not within sub-articular trabecular bone architecture"
Journal of Human Evolution, 2015
The description of acetabular shape variation among primates is essential for our understanding of the locomotor behaviour and ecology of both extant and fossil species. In this study, we use two-dimensional geometric morphometrics to examine variation in acetabular shape in human and non-human primates and to determine the degree to which it co-varies with locomotor behaviour, while taking both intra and inter-specific variation into account. To these ends, we examined the acetabulum of 303 left hip bones of 27 extant genera of primates (including humans) with different locomotor behaviours. After accounting for shape variation due to sex, size, and phylogeny, the results confirm that acetabular shape varies significantly across locomotor groups. The two most differentiated locomotor groups are leapers and slow-climbing quadrupeds, which exhibit a unique acetabular shape. Furthermore, the acetabulum of humans differed significantly from all other groups, while no significant differences existed between chimpanzees and gorillas. The most noticeable differences are detected in both cranial and dorsal areas and around the acetabular horns. This variation in acetabular morphology may have biomechanical implications at the level of the hip joint, potentially determining joint range motion and load distribution during locomotion. Given the increasing number of published studies on fossil pelves, our results are widely applicable to fossil analyses, with critical implications for paleoanthropological analyses about the complex locomotor behaviour of fossil specimens and their classification into locomotor groups, which may enhance our understanding of their ecological habits.
PLoS One
Understanding the mechanically-mediated response of trabecular bone to locomotion-specific loading patterns would be of great benefit to comparative mammalian evolutionary morphology. Unfortunately, assessments of the correspondence between individual trabecular bone features and inferred behavior patterns have failed to reveal a strong locomotion specific signal. This study assesses the relationship between inferred locomotor activity and a suite of trabecular bone structural features that characterize bone architecture. High-resolution computed tomography images were collected from the humeral and femoral heads of 115 individuals from eight anthropoid primate genera (Alouatta, Homo, Macaca, Pan, Papio, Pongo, Trachypithecus, Symphalangus). Discriminant function analyses reveal that subarticular trabecular bone in the femoral and humeral heads is significantly different among most locomotor groups. The results indicate that when a suite of femoral head trabecular features is considered, trabecular number and connectivity density, together with fabric anisotropy and the relative proportion of rods and plates, differentiate locomotor groups reasonably well. A similar, yet weaker, relationship is also evident in the trabecular architecture of the humeral head. The application of this multivariate approach to analyses of trabecular bone morphology in recent and fossil primates may enhance our ability to reconstruct locomotor behavior in the fossil record.
BMC Evolutionary Biology
Background: Morphological diversity of limb bone lengths, diameters, and proportions in mammals is known to vary strongly with locomotor habit. It remains less well known how different locomotor habits are correlated with cross-sectional traits of the limb skeleton, such as cross-sectional area (CSA), second moments of area (SMA), and section modulus (MOD) and whether these traits have evolved adaptively. CSA and SMA represent the bone's resistance to axial compression and bending, respectively, whereas MOD represents bone structural strength related to shape. Sampling 28 species of mustelids, a carnivoran lineage with diverse locomotor habits, we tested for differences in humeral, radial, and ulnar cross-sectional traits among specialists for climbing, digging, and swimming, in addition to generalists. Given that the limbs of digging specialists function in the dense substance of soil, and that swimming specialists need to counteract buoyancy, we predicted that these mustelids with these specializations should have the greatest values of cross-sectional traits. Results: We analyzed cross-sectional traits (calculated via μCT scanning and rendered dimensionless) in 5% increments along a bone's length and found significant differences among locomotor habits, though differences in ulnar cross-sectional traits were fewer than those for the humerus and radius. Swimming specialists had the greatest values of cross-sectional traits, followed by digging specialists. Climbing specialists had the lowest values of cross-sectional traits. However, phylogenetic affinity underlies these results. Fitting models of trait evolution to CSA and SMA revealed that a multi-rate Brownian motion model and a multi-optima Ornstein-Uhlenbeck model are the bestfitting models of evolution for these traits. However, inspection of α-values uncovered that many of the OU models did not differ from a Brownian motion model.
tWe assessed the influence of a variety of aspects of locomotion and ecology including gait and locomotortypes, maximal running speed, home range, and body size on postcranial shape variation in small tomedium-sized mammals, employing geometric morphometric analysis and phylogenetic comparativemethods. The four views analyzed, i.e., dorsal view of the penultimate lumbar vertebra, lateral view ofthe pelvis, posterior view of the proximal femur and proximal view of the tibia, showed clear phylogeneticsignal and interesting patterns of association with movement. Variation in home range size was relatedto some tibia shape changes, while speed was associated with lumbar vertebra, pelvis and tibia shapechanges. Femur shape was not related to any locomotor variables. In both locomotor type and high-speedgait analyses, locomotor groups were distinguished in both pelvis and tibia shape analyses. These resultssuggest that adaptations to both typical and high-speed gaits could explain a considerable portion ofthe shape of those elements. In addition, lumbar vertebra and tibia showed non-significant relationshipswith body mass, which suggests that they might be used in morpho-functional analyses and locomotorinferences on fossil taxa, with little or no bias for body size. Lastly, we observed morpho-functionalconvergences among several mammalian taxa and detected some taxa that achieve similar locomotorfeatures following different morphological paths.
Joint Loads in Marsupial Ankles Reflect Habitual Bipedalism versus Quadrupedalism
2013
Joint surfaces of limb bones are loaded in compression by reaction forces generated from body weight and musculotendon complexes bridging them. In general, joints of eutherian mammals have regions of high radiodensity subchondral bone that are better at resisting compressive forces than low radiodensity subchondral bone. Identifying similar form-function relationships between subchondral radiodensity distribution and joint load distribution within the marsupial postcranium, in addition to providing a richer understanding of marsupial functional morphology, can serve as a phylogenetic control in evaluating analogous relationships within eutherian mammals. Where commonalities are established across phylogenetic borders, unifying principles in mammalian physiology, morphology, and behavior can be identified. Here, we assess subchondral radiodensity patterns in distal tibiae of several marsupial taxa characterized by different habitual activities (e.g., locomotion). Computed tomography scanning, maximum intensity projection maps, and pixel counting were used to quantify radiodensity in 41 distal tibiae of bipedal (5 species), arboreal quadrupedal (4 species), and terrestrial quadrupedal (5 species) marsupials. Bipeds (Macropus and Wallabia) exhibit more expansive areas of high radiodensity in the distal tibia than arboreal (Dendrolagus, Phascolarctos, and Trichosurus) or terrestrial quadrupeds (Sarcophilus, Thylacinus, Lasiorhinus, and Vombatus), which may reflect the former carrying body weight only through the hind limbs. Arboreal quadrupeds exhibit smallest areas of high radiodensity, though they differ non-significantly from terrestrial quadrupeds. This could indicate slightly more compliant gaits by arboreal quadrupeds compared to terrestrial quadrupeds. The observed radiodensity patterns in marsupial tibiae, though their statistical differences disappear when controlling for phylogeny, corroborate previously documented patterns in primates and xenarthrans, potentially reflecting inferred limb use during habitual activities such as locomotion. Despite the complex nature of factors contributing to joint loads, broad observance of these patterns across joints and across a variety of taxa suggests that subchondral radiodensity can be used as a unifying form-function principle within Mammalia.
Zoological Journal of the Linnean Society, 2002
Traditionally a few limb proportions or total limb lengths have been regarded as indicative of peak running velocity. This is due to physical principles (inferred in-and outvelocities around the joints, stride lengths) and also the observation that fast-moving animals tend to share a number of purported key features which are either absent or not developed to near the same extent in slower moving forms. Previous studies have shown hind limb length and metatarsus/femur ratio to be correlated significantly, albeit modestly with running speed. These studies have nearly all been bivariate analyses. Based on the physical principles, there is reason to suppose that more variables than just m/f ratio could be important as adaptations for fast locomotion, and also that bivariate analyses are too simple. In this study a sample of 76 running mammals was used, with running speeds taken from literature. A number of osteological parameters were discovered to covary significantly with peak running speed, albeit only modestly. Using the information from phylogeny reduced all correlations, often significantly so. Multivariate analyses resulted in markedly higher correlation coefficients. Animals probably do not optimize their anatomy for the purpose of running very fast, which occurs only on rare occasions, but for reducing costs of locomotion.
Synopsis During locomotion over land, vertebrates' limb bones are exposed to loads. Like most biological structures, limb bones have a capacity to withstand greater loads than they usually experience, termed a safety factor (SF). How diverse are limb-bone SFs, and what factors correlate with such variation? We have examined these questions from two perspectives. First, we evaluated locomotor SF for the femur in diverse lineages, including salamanders, frogs, turtles, lizards, crocodilians, and marsupials (opossums). Comparisons with values for hind-limb elements in running birds and eutherian mammals indicate phylogenetic diversity in limb-bone SF. A high SF ($7) is primitive for tetrapods, but low magnitudes of load and elevated strength of bones contribute to different degrees across lineages; moreover, birds and eutherians appear to have evolved lower SFs independently. Second, we tested the hypothesis that SFs would be similar across limb bones within a taxon by comparing data from the humerus and femur of alligators. Both in bending and in torsion, we found a higher SF for the humerus than for the femur. Such a ''mixed chain'' of different SFs across elements has been predicted if bones have differing variabilities in load, different costs to maintain, or high SF values in general. Although variability in load is similar for the humerus and femur, a high SF may be less costly for the humerus because it is smaller than the femur. The high SFs of alligators also might facilitate differences in SF among their limb bones. Beyond these specific findings, however, a more general implication of our results is that evaluations of the diversity of limb-bone SFs can provide important perspective to direct future research. In particular, more complete understanding of variation in SF could provide insight into factors that promoted the evolutionary radiation of terrestrial locomotor function in vertebrates.