Some Locomotory Adaptations in Mammals.

Abstract

Summary. The pectoral girdle and fore limb of Equus and Dasypus are compared. It is shown that the shoulder muscles of the horse have a small mechanical advantage (1/13 for the m. teres major) and are therefore adapted to produce rapid movements of the limb; these muscles in the armadillo have a larger mechanical advantage (1/4 for the m. teres) to produce slower movements, while exerting a greater force. The broad scapulae and short legs of fossorial mammals are adaptations producing powerful movements of the foot, usually with strong abductor action. Aquatic mammals show similar modifications, though without the emphasis on abductor movements. The high, narrow scapulae and long legs of cursorial mammals are explained as adaptations to speed, though the detailed arrangements by which this is achieved differ in cursorial ungulates and carnivores. The sharp angles at the ends of the vertebral border of the scapula in cursorial ungulates provide pints of insertion for two parts of the m. serratus, which act as antagonists in the fore‐and‐aft movement of the shoulder. Similarly in the dog, and probably all cursorial carnivores and lagomorphs, the sharp vertebro‐axillary angle affords a point of insertion for the posterior digitations of the m. serratus. The mechanical adaptations of the olecranon process and the m. triceps are described. The structure of the vertebral column and axial musculature is shown to depend upon gait. Two types of gallop, the horse gallop and leaping gallop (e.g. dog) are analysed and the association between gait and structure described. The mechanics of gaits are discussed in an appendix. The extensor muscles from the pelvis to the femur fall into two groups, an iliac group adapted to rapid extension of the thigh, and an ischio‐pubic group adapted to slower but more powerful thigh extension. The relative proportions of the two regions of the pelvis vary according to the gaits adopted. In cursorial ungulates the ilium is long and the ischio‐pubic region short, whereas in aquatic mammals the latter region predominates. The lengths and cross‐sectional areas of the bones of the hind limb are shown to be correlated with gait in aquatic, cursorial (leaping gallop and horse gallop), saltatorial and graviportal mammals.

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

“…Body size, one of the most important biological variables (see Smith and Savage, 1955;Eisenberg, 1981;Hildebrand, 1988 Although they differ in methodology and results, all generated estimates exceeding 40 kg for some genera and 100 kg for others (Table 3). Such values place Santacrucian sloths, along with the extinct giant lemurs of Madagascar (Megaladapis and Archaeoindris, see Jungers et al, 2002), among the heavier extant climbing mammals.…”

Cynodont Postcranial Anatomy and the “Prototherian” Level of Mammalian Organization

“…However, if each of these bones is examined in detail important differences become apparent. The morphology of the monotreme scapula is quite unlike that in cynodonts; the substantial recurvature of the vertebral border is undoubtedly related to increasing the mechanical advantage of the teres major muscle, a common specialization in fossorial forms (see Smith and Savage, 1956). Furthermore, the rather flat monotreme scapula contrasts to the complex curvature of the cynodont scapula blade, a difference which cannot readily be explained.…”

Morphology and motion: hindlimb proportions and swing phase kinematics in terrestrially locomoting charadriiform birds

“…Taxa with more lightweight and distally light legs should possess lower locomotor costs and may attain higher speeds (Lull, 1904;Gregory, 1912;Howell, 1944;Smith and Savage, 1956;Gray, 1968;Gambaryan, 1974;Hildebrand, 1984Hildebrand, , 1985Hildebrand, , 1988Hildebrand and Hurley, 1985;Steudel, 1990;Wickler et al, 2004;Raichlen, 2005Raichlen, , 2006Browning et al, 2007). In contrast, taxa with more massive and distally heavy legs should incur higher locomotor costs or might be restricted to slower speeds of terrestrial locomotion (e.g.…”