Body mass in lowland gorillas: a quantitative analysis.

Body proportions and tissue composition (e.g., relative contributions of muscle, skin, bone, and adipose to total body mass) were determined through dissection of four adult captive lowland gorillas. The relative contribution of bone varies little among the four animals (10.2-13.4%) despite considerable range in body weights (99.5-211 kg). In tissue composition, three animals have on average 37.3% muscle relative to body mass. Maximum estimates of body fat range between 19.4-44%. Differences in age, sex, and life history events partially explain the observed variation in body proportions and tissue composition among the four animals. Although gorillas are considered extremely sexually dimorphic in body weight and canine size, differences in tissue are not as dramatic as body mass differences suggest. This study found sex differences mostly in the upper body; males have relatively heavier forelimbs, including heavier deltoid, trunk-binding, and deep back muscles compared to the younger female. The old, obese female had one half the muscle tissue of the other three animals (16% vs. 37.3%), and twice the body fat (44%); forelimbs and upper body musculature were relatively well-developed to compensate for the restricted hip-joint movement due to arthritis. Data on the variation in tissue composition and body proportions in gorillas provide a basis for comparison with other hominoids, including humans. For example, compared to highly dimorphic orangutans, gorillas have more muscle, less adipose tissue, lighter forelimbs and heavier hindlimbs. Such analyses complement studies of the skeleton and contribute to our understanding of human evolution and adaptation.

Hand abnormalities in pygmy chimpanzees (Pan paniscus).

Hand deformities in 2 wild-born pygmy chimpanzees were investigated through dissection, linear measurements, bone mineral analysis and X-rays. Weight of tissue (skin, muscle, bone) was determined for each body segment (hand, forearm, upper arm), permitting comparison between the abnormal and normal upper limbs. In one individual, the right and left forearms and hands differed in tissue weights and bone mineral content. In the other, the hands differed in tissue composition, but not the forearms.

Skeletal differences between pygmy (Pan paniscus) and common chimpanzees (Pan troglodytes).

Skeletal dimensions of pygmy (Pan paniscus) and common (Pan troglodytes) chimpanzees were compared. Significant differences were found in the clavicles, scapulae, pelvises, and in the humerus/femur and femur head/length ratios. No significant differences were observed in long bone lengths or talar breadths. There is extensive overlap in body weights, so that the observed differences cannot be accounted for by body size alone. We conclude that pygmy and common chimpanzees are morphologically distinct. Implications for hominoid evolution are discussed.