Unique suites of trabecular bone features characterize locomotor behavior in human and non-human anthropoid primates

Abstract

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.

Figure 1. Volume of interest (VOI) selection method.

The articular surface of the humeral and femoral heads (shown in red) were extracted from a three-dimensional isosurface reconstruction. The volume of interest was scaled based on the size of a best-fit cube for the articular surface and was positioned in the center of the humeral or femoral head.

Figure 2. Results of multivariate discriminant function analyses for the femoral head.

Symbols: red triangles, bipeds; blue squares, terrestrial quadrupeds; orange diamonds, arboreal quadrupeds; black and white squares, arboreal quadruped-climbers; cyan hexagons, quadrumanous climbers; brown triangles, brachiators; purple circles, terrestrial quadruped-climbers.

Figure 3. Results of multivariate discriminant function analyses for the humeral head.

Symbols as in Figure 2.

Figure 4. Three-dimensional reconstructions of cubic trabecular bone specimens from the humerus (top) and femur (bottom) from individuals used in the current study.

Note variation in trabecular architecture between the femur and humerus, and among taxa.