Functional Anatomy and Adaptation of Male Gorillas (Gorilla gorilla gorilla) With Comparison to Male Orangutans (Pongo pygmaeus)

Abstract

Great apes diversified during the Miocene in Old World forests. Two lineages, gorillas in Africa and orangutans in Asia, have sexual dimorphisms of super-sized males, though they presumably diverged from a smaller common ancestor. We test the hypothesis that they increased in body mass independently and convergently, and that their many postcranial differences reflect locomotor differences. Whole body dissections of five adult male gorillas and four adult male orangutans allowed quantification of body mass distribution to limb segments, of body composition (muscle, bone, skin, and fat relative to total body mass), and of muscle distribution and proportions. Results demonstrate that gorilla forelimb anatomy accommodates shoulder joint mobility for vertical climbing and reaching while maintaining joint stability during quadrupedal locomotion. The heavily muscled hind limbs are equipped for propulsion and weight-bearing over relatively stable substrates on the forest floor. In contrast, orangutan forelimb length, muscle mass, and joint construction are modified for strength and mobility in climbing, bridging, and traveling over flexible supports through the forest canopy. Muscles of hip, knee, and ankle joints provide rotational and prehensile strength essential for moving on unstable and discontinuous branches. We conclude that anatomical similarities are due to common ancestry and that differences in postcranial anatomy reflect powerful selection for divergent locomotor adaptations. These data further support the evolutionary conclusion that gorillas fall with chimpanzees and humans as part of the African hominoid radiation; orangutans are a specialized outlier. Anat Rec, 294:1842Rec, 294: -1855Rec, 294: , 2011. V V C 2011 Wiley-Liss, Inc.

Body composition in Pan paniscus compared with Homo sapiens has implications for changes during human evolution

“…Individual paniscus female 3 (PF3) had no offspring or pregnancies during her life, had remarkably low levels of dissectible fat, and stood out as having the highest percentage of muscle mass among the females (44.1%, Table 1). Body fat is also sexually dimorphic in some monkeys, as well as in gorillas and orangutans (23)(24)(25), and has a demonstrated role in reproduction (54)(55)(56). The same is true for H. sapiens (19,(43)(44)(45)(46)(47)(48).…”

“…Skin. African apes' hairy skin constitutes between 10% and 16% of their total body mass (24,25). Long hair shafts and follicles grow in a relatively thick epidermis.…”

“…From each segment, the major tissues (skin, muscle, and bone) are separated and weighed immediately (24,25,87). Muscle mass encompasses all skeletal muscle from the limbs, torso, and masticatory muscles.…”

“…Few such comparative data are available on apes (but cf. [22][23][24][25]. The rarity of apes in captivity, their long lives, and the logistics of obtaining relatively complete bodies for dissection pose challenges for accumulating a comparative sample.…”

How forelimb and hindlimb function changes with incline and perch diameter in the green anole,Anolis carolinensis

“…Structural differences between the forelimbs and the hindlimbs have been well documented among vertebrates; the pectoral girdle is generally more mobile than the pelvic girdle and structural differences between the glenoid cavity and the acetabulum lead to the potential for a greater range of motion in the forelimb than in the hindlimb (Haines, 1952;Snyder, 1954;Peterson, 1971;Peterson, 1973;Peterson, 1974;Jenkins and Goslow, 1983;Peterson, 1984;Reynolds, 1985;Schmitt, 1994;Larson et al, 2001;Lammers, 2007;Zihlman et al, 2011). In most primates, the shallow glenoid cavity with reduced coracoid and acromion processes in the pectoral girdle compared with the deeper acetabulum of the pelvic girdle are likely related, in part, to the greater weightbearing function of the hindlimbs relative to the mobile forelimbs (Reynolds, 1985;Zihlman et al, 2011). These structural differences between forelimbs and hindlimbs tend to be most exaggerated in arboreal species, including primates (Larson et al, 2000), with some of the most extreme examples found in lizards.…”