EGI, N; Kyoto Univ. Primate Research Inst., Inuyama, Japan: Limb bone morphology in carnivores and its relationship to locomotor behavior and body size

Morphologies of limb bones are known to be affected by animal’s locomotion and body size. This study examines variation of bone lengths and mid-shaft cross-sectional properties of humerus, femur, and tibia, and humeral and femoral articular volumes and surface areas among 47 species of small to medium sized carnivorans and carnivorous marsupials. The sample species are classified into four locomotor groups. Several differences in bone dimensions exist among the locomotor groups: cursors have longer and lightly built limb bones, larger articular volumes relative to surface areas, and restriction to parasagittal movement in the elbow joint, and arborealists indicate relatively larger mobility of joints and greater shaft rigidities. Non-cursorial terrestrialists except larger semi-fossorial forms tend to have shorter limbs and low shaft rigidities. Scansors are intermediate between the others in their bone structure. Allometry of the limb bone dimensions against body mass are not significant except that humeral shaft rigidity and tibial length scale positively and negatively in semi-fossorial terrestrialists, respectively. In general, as body size increases, humeri and tibiae get more robust relative to femora, and distal humeral articulation and femroal head become larger relative to humeral head and distal femoral condyles, respectively. These may relate to changes in limb posture and joint mobilities. Finally, marsupials differ from carnivorans in having small medullary cavities relative to shaft cross-section, small articular volumes relative to surface areas, smaller articulations relative to body mass and shaft rigidities, and smaller tibial shaft rigidities. These characters may represent retention of primitive traits in marsupials or reflect postual differences.