Cross-Sectional Morphology of the Femoral Neck of Wild Chimpanzees

Abstract

To understand the mechanical effects of different modes of locomotion on the femoral neck of chimpanzees, we investigated the cross-sectional morphology of the femoral neck of 4 chimpanzees (Pan troglodytes schweinfurthii) collected from the Mahale Mountains, Tanzania. We performed serial computed tomography (CT) scans of the neck from the femoral head to the base of the neck perpendicular to the long axis of the neck. We measured the cortical thickness of the serial 5 cross sections of the neck region every 45°around the circumference, i.e., 8 points per section, and examined the cross-sectional properties of the mid-section. When we compared the superior and inferior parts of the cortical thickness of the femoral neck, the inferior part exhibited the greatest cortical thickness whereas the superior part had the smallest values in every specimen. Researchers have also observed such regional differences between superior and inferior cortical thicknesses in bipedal humans and other primates, although these differences are not as large in the chimpanzee as in bipedal hominini. The present study differed from the past study on hominini and chimpanzees in that the superior anterior (SA) part exhibited greater cortical thickness in chimpanzees. We believe these observations reflect the structural strengthening of parts of the chimpanzee femoral neck that is needed to accommodate the mechanical loads imposed by arboreal vertical climbing and terrestrial quadrupedal and bipedal locomotion.

Bilateral Asymmetry of Humeral Torsion and Length in African Apes and Humans

“…This seems to be in line with previous studies, which suggest that lengths are less sensitive to mechanical stimuli than other traits [Steele and Mays, 1995;Steele, 2000b;Auerbach and Ruff, 2006]. However, while the strength and shape of cross-sectional morphology have been associated with bone responses to loading regimes throughout life [Ruff, 1990;Ruff et al, 1993;Stock and Pfeiffer, 2001;Matsumura et al, 2002;Lieberman et al, 2003;Marchi, 2007Marchi, , 2008Shaw and Stock, 2009a, b;Matsumura et al, 2010], humeral torsion does not continue to develop past fusion of the proximal epiphysis [Krahl, 1976]. We postulate that it is the degree of sensitivity of the epiphyseal cartilage to biomechanical stimuli, as well as its speed of response and the timing of epiphyseal growth during formative adolescence (90% of epiphyseal growth occurs between 11 and 20 years of age in humans [Osbahr et al, 2002]), that are responsible for these asymmetries.…”

Brief communication: Paleobiological inferences on the locomotor repertoire of extinct hominoids based on femoral neck cortical thickness: The fossil great ape hispanopithecus laietanus as a test‐case study

“…However, instead of distinguishing bipeds from other primates, as noted by other researchers (Rafferty, 1998;Demes et al, 2000;Matsumura et al, 2010a), this trait much more clearly enables distinguishing arboreal taxa with a significant suspensory component from both quadrupedal and bipedal taxa. However, instead of distinguishing bipeds from other primates, as noted by other researchers (Rafferty, 1998;Demes et al, 2000;Matsumura et al, 2010a), this trait much more clearly enables distinguishing arboreal taxa with a significant suspensory component from both quadrupedal and bipedal taxa.…”

“…The distribution of cortical thickness at the femoral neck among extant primates is related to their positional behavior, and thus can be employed for inferring the locomotor repertoire of fossil primates. However, instead of distinguishing bipeds from other primates, as noted by other researchers (Rafferty, 1998;Demes et al, 2000;Matsumura et al, 2010a), this trait much more clearly enables distinguishing arboreal taxa with a significant suspensory component from both quadrupedal and bipedal taxa. Although this feature should not be used to make paleobiological inferences on locomotion without taking into account other morphological features, its usefulness in this respect is illustrated by the condition displayed by the fossil great ape Hispanopithecus laietanus.…”

“…These bipedal taxa display a superior cortex thinner than the inferior one (Ohman et al, 1997;Demes et al, 2000;Lovejoy et al, 2002), thus contrasting with the more homogeneous cortical thickness of extant great apes, which possess thicker inferior and especially superior cortices relative to the bipeds, resulting in a uniform supero-inferior ratio closer to 1 along the neck (Ohman et al, 1997). When a more comprehensive primate sample is taken into account, however, it emerges that humans largely overlap with most other locomotor groups, with the exception of knuckle-walkers and specialized suspensory taxa when index and intrinsic proportions are taken into account (Rafferty, 1998;Demes et al, 2000;Matsumura et al, 2010a). According to our results, two different patterns of distribution of cortical thickness at the femoral neck can be distinguished among extant primates, being functionally attributable to differences in the direction of weight transfer through the femur and, consequently, to different loading stresses experienced by this bone depending on the type of locomotion (Scherf, 2008).…”

A three‐dimensional axis for the study of femoral neck orientation

“…; Rafferty, ; Matsumura et al. ). Moreover, the trabecular bone of the proximal part of the femur is organised along three major trabecular systems (medial, trochanteric and arcuate; Skuban et al.…”