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1. Baby steps towards linking calcaneal trabecular bone ontogeny and the development of bipedal human gait

   https://doi.org/10.1111/joa.13120  

   Saers, Jaap P. P. ; Ryan, Timothy M. ; Stock, Jay T. ( November 2019 , Journal of Anatomy)

   Trabecular bone structure in adulthood is a product of a process of modelling during ontogeny and remodelling throughout life. Insight into ontogeny is essential to understand the functional significance of trabecular bone structural variation observed in adults. The complex shape and loading of the human calcaneus provides a natural experiment to test the relationship between trabecular morphology and locomotor development. We investigated the relationship between calcaneal trabecular bone structure and predicted changes in loading related to development of gait and body size in growing children. We sampled three main trabecular regions of the calcanei using micro‐computed tomography scans of 35 individuals aged between neonate to adult from the Norris Farms #36 site (1300 AD, USA) and from Cambridge (1200–1500 AD, UK). Trabecular properties were calculated in volumes of interest placed beneath the calcaneocuboid joint, plantar ligaments, and posterior talar facet. At birth, thin trabecular struts are arranged in a dense and relatively isotropic structure. Bone volume fraction strongly decreases in the first year of life, whereas anisotropy and mean trabecular thickness increase. Dorsal compressive trabecular bands appear around the onset of bipedal walking, although plantar tensile bands develop prior to predicted propulsive toe‐off. Bone volume fraction and anisotropy increase until the age of 8, when gait has largely matured. Connectivity density gradually reduces, whereas trabeculae gradually thicken from birth until adulthood. This study demonstrates that three different regions of the calcaneus develop into distinct adult morphologies through varying developmental trajectories. These results are similar to previous reports of ontogeny in human long bones and are suggestive of a relationship between the mechanical environment and trabecular bone architecture in the human calcaneus during growth. However, controlled experiments combined with more detailed biomechanical models of gait maturation are necessary to establish skeletal markers linking growth to loading. This has the potential to be a novel source of information for understanding loading levels, activity patterns, and perhaps life history in the fossil record.

    

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2. Footloose: Articular surface morphology and joint movement potential in the ankles of lorisids and cheirogaleids

   https://doi.org/10.1002/ajpa.24298  

   Yapuncich, Gabriel S. ; Granatosky, Michael C. ( April 2021 , American Journal of Physical Anthropology)

   The competing functional demands of diarthrodial joints, permitting mobility while retaining enough stability to transmit forces across the joint, have been linked with the shape and size of the joint's articular surfaces. A clear understanding of the relationship between joint morphology and joint movement potential is important for reconstructing locomotor behaviors in fossil taxa.

   In a sample of matched tali and calcanei of lorisids (n = 28) and cheirogaleids (n = 38), we quantify the surface areas of the talar and calcaneal ectal (=posterior talocalcaneal) articular surfaces and model the principal curvatures of these surfaces with quadric formulas. These two taxonomic groups have similar body masses, but differ substantially in positional behavior, so that differences in joint surface morphology should reflect adaptive demands of their locomotor behavior.

   Compared with cheirogaleids, lorisids exhibit: (a) a significantly greater area difference between their paired joint surfaces; and (b) a more pronounced saddle shape for the talar ectal facet.

   The increased subtalar joint mobility observed in lorisids may be achieved by increasing the amount of sliding and rolling that can occur at the subtalar joint. The subtalar joint morphology observed in two fossil euarchontans, the plesiadapiformsPurgatoriussp. andPlesiadapis cookei, compares favorably with the morphology observed among lorisids, potentially suggesting antipronograde postures within these extinct taxa.

    

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3. Scaling and relative size of the human, nonhuman ape, and baboon calcaneus

   https://doi.org/10.1002/ar.24642  

   Harper, Christine M. ; Ruff, Christopher B. ; Sylvester, Adam D. ( April 2021 , The Anatomical Record)

   Among human and nonhuman apes, calcaneal morphology exhibits significant variation that has been related to locomotor behavior. Due to its role in weight‐bearing, however, both body size and locomotion may impact calcaneal morphology. Determining how calcaneal morphologies vary as a function of body size is thus vital to understanding calcaneal functional adaptation. Here, we study calcaneus allometry and relative size in humans (n = 120) and nonhuman primates (n = 278), analyzing these relationships in light of known locomotor behaviors. Twelve linear measures and three articular facet surface areas were collected on calcaneus surface models. Body mass was estimated using femoral head superoinferior breadth. Relationships between calcaneal dimensions and estimated body mass were analyzed across the sample using phylogenetic least squares regression analyses (PGLS). Differences between humans and pooled nonhuman primates were tested using RMA ANCOVAs. Among (and within) genera residual differences from both PGLS regressions and isometry were analyzed using ANOVAs with post hoc multiple comparison tests. The relationships between all but two calcaneus dimensions and estimated body mass exhibit phylogenetic signal at the smallest taxonomic scale. This signal disappears when reanalyzed at the genus level. Calcaneal morphology varies relative to both body size and locomotor behavior. Humans have larger calcanei for estimated body mass relative to nonhuman primates as a potential adaptation for bipedalism. More terrestrial taxa exhibit longer calcaneal tubers for body mass, increasing the triceps surae lever arm. Among nonhuman great apes, more arboreal taxa have larger cuboid facet surface areas for body mass, increasing calcaneocuboid mobility.

    

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4. Phylogenetic and environmental effects on limb bone structure in gorillas

   https://doi.org/10.1002/ajpa.23437  

   Ruff, Christopher B. ; Burgess, M. Loring ; Junno, Juho‐Antti ; Mudakikwa, Antoine ; Zollikofer, Christophe P. E. ; Ponce de León, Marcia S. ; McFarlin, Shannon C. ( February 2018 , American Journal of Physical Anthropology)

   The effects of phylogeny and locomotor behavior on long bone structural proportions are assessed through comparisons between adult and ontogenetic samples of extant gorillas.

   A total of 281 wild‐collected individuals were included in the study, divided into four groups that vary taxonomically and ecologically: western lowland gorillas (G. g. gorilla), lowland and highland grauer gorillas(G. b. graueri), and Virunga mountain gorillas (G. b. beringei). Lengths and articular breadths of the major long bones (except the fibula) were measured, and diaphyseal cross‐sectional geometric properties determined using computed tomography. Ages of immature specimens (n = 145) were known or estimated from dental development. Differences between groups in hind limb to forelimb proportions were assessed in both adults and during development.

   Diaphyseal strength proportions among adults vary in parallel with behavioral/ecological differences, and not phylogeny. The more arboreal western lowland and lowland grauer gorillas have relatively stronger forelimbs than the more terrestrial Virunga mountain gorillas, while the behaviorally intermediate highland grauer gorillas have intermediate proportions. Diaphyseal strength proportions are similar in young infants but diverge after 2 years of age in western lowland and mountain gorillas, at the same time that changes in locomotor behavior occur. There are no differences between groups in length or articular proportions among either adults or immature individuals.

   Long bone diaphyseal strength proportions in gorillas are developmentally plastic, reflecting behavior, while length and articular proportions are much more genetically canalized. These findings have implications for interpreting morphological variation among fossil taxa.

    

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5. Long bone diaphyseal shape follows different ontogenetic trajectories in captive and wild gorillas

   https://doi.org/10.1002/ajpa.23636  

   Canington, Stephanie L. ; Sylvester, Adam D. ; Burgess, M. Loring ; Junno, Juho‐Antti ; Ruff, Christopher B. ( August 2018 , American Journal of Physical Anthropology)

   A number of studies have demonstrated the ontogenetic plasticity of long bone diaphyseal structure in response to mechanical loading. Captivity should affect mechanical loading of the limbs, but whether captive apes grow differently than wild apes has been debated. Here, we compare captive and wild juvenile and adultGorillato ascertain whether growth trajectories in cross‐sectional diaphyseal shape are similar in the two environments.

   A sample of young juvenile (n = 4) and adult (n = 10) captiveGorilla gorillagorillaspecimens, with known life histories, were compared with age‐matched wildG.g. gorilla(n = 62) andG. beringei beringei(n = 75) in relative anteroposterior to mediolateral bending strength of the femur, tibia, and humerus. Cross sections were obtained using peripheral quantitative CT.

   Captive and wild adultG.g. gorilladiffered in bending strength ratios for all three bones, but these differences were not present in young juvenileG.g. gorilla. In comparisons across taxa, captive juvenileG.g. gorillawere more similar to wildG.g. gorillathan toG.b. beringei, while captive adultG.g. gorillawere more similar in shape toG.b. beringeiin the hind limb.

   Captive and wildG. gorillafollow different ontogenetic trajectories in long bone diaphyseal shape, corresponding to environmental differences and subsequent modified locomotor behaviors. Differences related to phylogeny are most evident early in development.

    

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