Trabecular architecture of the capitate and third metacarpal through ontogeny in chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla).

Chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) both knuckle-walk in adulthood but are known to develop their locomotor strategies differently. Using dentally defined age-groups of both Pan and Gorilla and behavioral data from the literature, this study presents an internal trabecular bone approach to better understand the morphological ontogeny of knuckle-walking in these taxa. Capitate and third metacarpal bones were scanned by µCT at 23-43 µm resolution with scaled volumes of interest placed centrally within the head of the capitate and base of the third metacarpal. Trabecular measures related to activity level (size-adjusted bone volume/total volume, trabecular number, and bone surface area/bone volume) met expectations of decreasing through ontogeny in both taxa. Degree of anisotropy did not show statistical support for predicted species differences, but this may be due to the sample size as observed changes through ontogeny reflect expected trends in the capitate. Analyses of principal trabecular orientation corroborated known behavioral differences related to variation of hand use in these taxa, but only Pan showed directional patterning associated with suggested wrist posture. Assessment of allometry showed that the trabecular bone of larger animals is characterized by fewer and thinner trabeculae relative to bone size. In combination, these findings confirm the efficacy of trabecular bone in reflecting locomotor ontogeny differences between closely related taxa. These techniques show promise for use within the hominin fossil record, particularly for taxa hypothesized to be arboreal in some capacity.

A molar microwear texture analysis of pitheciid primates.

Dental microwear textures have been examined for a broad range of extant primates to assess their efficacy for reconstructing diets of fossil species. To date though, no dental microwear texture data have been published for pitheciid molars, despite reported variation in degree of sclerocarpy and, by extension, the fracture properties of foods these platyrrhines eat. While all pitheciids eat hard or tough seeds, Chiropotes and Pithecia have been documented to consume more than Callicebus. In this study, we explored whether measures of molar microwear texture complexity discriminate taxa following variation in reliance upon seeds, and whether dispersion among variables is greatest in Callicebus, which has the most variable diet. Here we report results for a study of microwear textures on M2 "Phase II" facets of Ch. satanas (N = 14), P. irrorata (N = 8), and Ca. moloch (N = 24) from the Brazilian Amazon (Oriximina, UHE Samuel, and Taperinha, respectively). Textures examined using a scanning confocal profiler showed significant differences in central tendencies for three measures: mean dale area (Sda), anisotropy (Str), and heterogeneity (HAsfc9 ). Ten measures showed significant differences in dispersion, with Callicebus being significantly more variable in eight of those ten. These results demonstrate that the pitheciids with different morphological adaptations and dietary reliance on seeds differ in their dental microwear textures, though less than initially hypothesized. Measures of dispersion, especially, show potential for identifying dietary variability.