Trabecular Ontogeny of the Gorilla Third Metacarpal

The trabecular bone morphology of adult extant primates has been shown to reflect mechanical loading patterns related to locomotion. However, ontogenetic studies of humans and other mammal species has shown that there may be an adaptive lag between trabecular response and current mechanical loading patterns, which could result in adult trabecular bone morphology reflecting juvenile behaviours. This study investigated ontogenetic changes in the trabecular bone structure of the third metacarpal of mountain (n = 26) and western lowland gorillas (n = 26) and its relationship to changes in loading patterns. Results show that trabecular bone reflects mechanical loading throughout ontogeny. Bone volume fraction, trabecular thickness,and trabecular number are low at birth and increase with age. Degree of anisotropy was variable throughout ontogeny and showed no clear pattern. A high concentration of bone volume fraction can be observed on the palmar side of the third metacarpal in early life, reflecting the high frequency of climbing, suspensory, and play behaviours of young gorillas. This concentration moves to the dorsal side as terrestrial knucklewalking becomes the primary form of locomotion around 5 years of age. Fusion of the epiphysis often did not take place until 8 - 12 years of age, and overall trabecular patterning did not fully reflect adult patterns until fusion was complete, suggesting there is a lag between adult-like behaviours and adult-like trabecular morphology. No differences were found between mountain and western lowland gorillas.