Anatomy and development of the koala, Phascolarctos cinereus: an evolutionary perspective on the superfamily Vombatoidea.

Fifteen koalas (Phascolarctos cinereus)--5 pouched young from 4 to 6.5 months and 10 adults from 5 to 16.5 years--were analyzed for functional parameters (body composition, limb segment and muscle mass, post-cranial skeletal characters) and developmental expressions (growth of body, brain, musculature). These data were compared with a convergent eutherian, the three-toed sloth, Bradypus infuscatus, and with the koala's distant (Macropodid; wallabies) and proximate (Vombatid; wombats) marsupial relatives. Musculoskeletal structures correlated with sitting and climbing; the growth of the young and the physiological demands of adulthood correlated with the low-quality diet of Eucalyptus foliage. The gestalt of the ancestral Vombatoids (pronograde quadrupeds, generalist browsers and social conservatives with low basal metabolism and attenuated development) provided the baseline essential for their locomotor and nutritional divergence into arboreal browsers, the koalas, and fossorial grazers, the wombats.

How muscle mass is part of the fabric of behavioral ecology in East African bovids (Madoqua, Gazella, Damaliscus, Hippotragus).

Tissue composition and the distribution of body mass are described for four genera of East African Bovidae (Madoqua, Gazella, Damaliscus, Hippotragus) with supporting data from four others (Neotragus, Oryx, Tragelaphus, Connochaetes). These species are high in muscle mass, an adaptation convergent with other high-speed terrestrial cursors, bounders, and saltators. The segments below the elbow/cubitus and knee/stifle/genu joints in small bovids are both lighter in percent of total body mass (8.6% TBM) and less heavily muscled (10-15% of total limb musculature) than those segments in macaques (13.6% TBM, 20-25% of the limb musculature). Bovid species differ from one another in the regional distribution of muscle mass. Madoqua kirkii (4-5 kg) concentrates muscle in the lumbar extensors and hindlimbs; large species such as Damaliscus doreas (50-60 kg) and Hippotragus niger (160-220 kg) distribute it more evenly between the lumbar and cervical regions and between the hindlimbs and forelimbs. Gazella dorcas (10-20 kg) is quantitatively intermediate in those characteristics. The redistribution of muscle mass with increasing size correlates with the loss of axial bending of the vertebral column: in small, hindlimb dominant, 'dorsomobile' species such as Madoqua sagittal mobility increases stride length through 'extended' suspension; in large 'dorsostable' species such as Damaliscus and Hippotragus the vertebral column resists bending, consequently abbreviating or omitting this non-contact phase of the gait cycle. Locomotor adaptation as it is reflected in size, shape, and musculoskeletal structure is the key to habitat choice, dietary specialization, social structure, and male agonistic behavior and, therefore, central to the fabric of behavioral ecology.

Body composition and the evolution of the Macropodidae (Potorous, Dendrolagus, and Macropus).

The segmental distribution of body weight and the proportions of skin, muscle, and bone are compared for three genera of the Macropodidae (Potorous, Dendrolagus, and Macropus) and one genus of the Petauridae (Pseudocheirus). Potorous and Macropus possess high proportions of muscle mass to total body weight, high concentrations of musculature in the lumbar extensors, thigh, and tail, and disproportionate ratios of forelimb: hindlimb bone and forelimb: hindlimb muscle which correspond to disproportions of intermembral length. These species converge with high-speed terrestrial runners in some traits and remain distinctive in others. Macropus, larger, more muscular, and faster than Potorous, appears to store and return energy to the hopping cycle more efficiently. Dendrolagus has less than three-fourths the musculature of the other macropod genera, low proportions of the back extensor muscles compared to the other macropods, and relatively more equal ratios of forelimb:hindlimb bone and forelimb:hindlimb muscle. This species converges with slow-moving arboreal climbers such as Pseudocheirus. These data on body mass and tissue proportions translate directly into center of gravity, strength-to-weight ratio, and muscular (kinetic) chains, key elements of macropod evolution. The geometric similarity of muscle between smaller potoroids and larger macropodids, and assumption critical to allometric comparison, is not confirmed.

Body weight: its relation to tissue composition, segment distribution, and motor function. I. Interspecific comparisons.

The composition of skin, muscle, and bone and their distribution throughout the body are compared for "advanced" or "specialized" species (Alouatta, Macaca, Canis, Felis, Lepus); smaller, more closely related species (Tupaia and the Lorisidae); and several species within the same ecosystem (Barro Colorado Island, Panama). Among the most significant variables, the skin of sloths, howlers and macaques constitutes more than 12% of body weight, whereas greyhound skin is 5% of weight; sloth and howler muscle are 25% of weight, macaque muscle about 40% of weight, greyhound and agouti muscle over 50% of weight. In tree shrews and galagos muscle is heavier (35%) than in pottos and slow lorises (below 28%), but bone and skin are lighter. All species differ in the segmental distribution of weight. Cats have light tails, light feet and heavy thighs, whereas howlers have heavy tails, heavy feet, and light thighs. The galagos have heavy hindlimbs and tails, the pottos and lorises have reduced tails and approximately equal fore- and hindlimbs. Convergences in segment pattern (sloths with pottos and lorises, marmosets with tree shrews, owl monkeys with galagos, cebus with macaques) as well as divergences are documented. All weight-of tissue and weight-of-segment variables are correlated directly with locomotor adaptation.

Body weight: its relation to tissue composition, segment distribution, and motor function. II. Development of Macaca mulatta.

The relative composition of skin, muscle, and bone and their distribution patterns throughout the body are given for a series of Macaca mulatta from 171 days conceptual age through adulthood. In terms of percent of total body weight, the musculature of these animals doubles during the firs postnatal year whereas bone and skin decrease. Regionally, the muscles of the thighs, back extensors, truncal-forelimb and upper arms increase most markedly. The thighs double and the upper arms increase whereas the trunk, hands, feet, and tail decrease. The biomechanical implications of these changes for motor development are discussed.