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Abstract Understanding the functional significance of morphological variation is crucial for investigating locomotor adaptations in fossil primates and early hominins. However, the nuanced form–function relationship in the upper limbs of extant apes is difficult to discern due to their varied locomotor behaviors, complicating the interpretation of similar features in fossil hominins. Trabecular bone, which responds to mechanical strain, reflects the intensity and direction of forces during movement, making it valuable for identifying locomotor adaptations in hominoids. This study examines trabecular bone in the clavicle—a crucial component of shoulder biomechanics—to explore its relationship to mechanical loading patterns and bone functional adaptations in primate locomotion. Using a whole‐bone approach, we analyzed trabecular structure in the clavicle of apes:Gorillaspp. (G. beringei:N = 28;G. gorilla:N = 29),Homo sapiens(N = 19),Hylobatesspp. (H. lar:N = 28;H. concolor:N = 3),Pongospp. (P. abelii:N = 13;P. pygmaeus:N = 24), andPan troglodytes(N = 35), quantifying relative bone volume fraction (rBV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and trabecular number (Tb.N) from high‐resolution micro‐CT scans. Aspects of the clavicular trabecular architecture among ape taxa appear to correspond to differences in locomotor behavior. In most taxa, rBV/TV is highest in regions underlying muscle attachment sites frequently used during upper limb activities, with differences among taxa predominantly reflecting variations in upper limb use and muscle attachment sites. Regions of high rBV/TV beneath entheses and articular surfaces result from different trabecular parameters—higher rBV/TV is achieved primarily via greater Tb.Th under entheses, while in subarticular regions, it is driven by higher Tb.N. However, no consistent differences in sternoclavicular subarticular trabecular bone emerge betweenHomoand the other apes, despite differences in shoulder positioning on the torso. Muscle activity appears to significantly influence trabecular bone structure in the clavicle of living apes, with implications for reconstructing early hominin locomotor behaviors and upper limb use.
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Interspecific Variation of Calcaneal Morphology in Gorillas
The foot plays a prominent role in weight-bearing suggesting it may reflect locomotor variation. Despite the immense amount of foot research, the calcaneus has been relatively understudied. Here we analyzed the entire calcaneal shape of Gorilla gorilla gorilla (n=41), Gorilla beringei graueri (n=17) and Gorilla beringei beringei (n=8) to understand how morphology relates to locomotor behavior. Calcanei were surface scanned and external shape analyzed using a three-dimensional geometric morphometric sliding semilandmark analysis. Semilandmarks were slid to minimize the bending energy of the thin plate spline interpolation function relative to the updated Procrustes average. Generalized Procrustes Analysis was used to align landmark configurations and shape variation was summarized using a principal components analysis. Procrustes distances between species were calculated and resampling statistics were run to test for group differences. All subspecies demonstrate statistically different morphologies (p<0.005 for pairwise comparisons). G. b. graueri separates from other subspecies based on posterolateral morphology, with G. b. graueri demonstrating an elongated peroneal trochlea, and thus more bone superiorly than G. g. gorilla. Compared to G. b. beringei, G. b. graueri has less bone inferiorly near the tuberosity. Cuboid and posterior talar facet shapes correlate with arboreality. G. b. beringei (most terrestrial) has a flatter cuboid facet and a more transversely oriented/relatively smaller posterior talar facet than G. g. gorilla (most arboreal) and G. b. graueri represents an intermediate morphology. These differences demonstrate a relationship between calcaneal shape and locomotor behavior and suggest that G. b. graueri may load its foot differently from the other subspecies. This project was supported by NSF grant # BCS - 1824630.
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- Award ID(s):
- 1824630
- PAR ID:
- 10104810
- Date Published:
- Journal Name:
- American journal of physical anthropology
- Volume:
- 168
- Issue:
- S68
- ISSN:
- 0002-9483
- Page Range / eLocation ID:
- 98
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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