Locomotor and postural development of wild chimpanzees.

Chimpanzees are our closest living relatives and their positional repertoire likely includes elements shared with our common ancestor. Currently, limitations exist in our ability to correlate locomotor anatomy with behavioral function in the wild. Here we provide a detailed description of developmental changes in chimpanzee locomotion and posture. Fieldwork was conducted on wild chimpanzees at Ngogo, Kibale National Park, Uganda. The large size of the Ngogo chimpanzee community permitted cross-sectional analysis of locomotor and postural changes across many individuals. Chimpanzee positional behavior proceeds developmentally through a number of distinct stages, each characterized by its own loading regime. Infants principally used their upper limbs while moving; the loading environment changed to more hindlimb dominated locomotion as infants aged. Infants displayed more diversity in their forms of positional behavior than members of any other age-sex class, engaging in behaviors not habitually exhibited by adults. While the most common locomotor mode for infants was torso-orthograde suspensory locomotion, a large shift toward quadrupedal locomotion during infancy occurred at three years of age, when rates of this behavior increased. Overall, the most dramatic transition in positional behavior occurred during juvenility (at approximately five years), with the advent of complete independent locomotion. Juveniles decreased the amount of time they spent clinging and in torso-orthograde suspensory locomotion and increased their time spent sitting and walking and running quadrupedally compared with younger individuals. Juvenility marked the age at which quadrupedal walking became the most frequent locomotor behavior, but quadrupedal walking did not encompass the majority of locomotor time until individuals reached adolescence. Relative to all younger individuals, adolescent chimpanzees (10-13 years) experienced a further increase in the amount of time they walked quadrupedally. Locomotor behavior did not reach adult form until adolescence, closer to the time of epiphyseal fusion than previously thought. These findings provide new data to make predictions about how behavioral transitions influence skeletal change.

Postcranial functional morphology of Morotopithecus bishopi, with implications for the evolution of modern ape locomotion.

The large-bodied hominoid from Moroto, Uganda has until recently been known only from proconsulid like craniodental remains and some vertebrae with modern ape like features. The discovery of two partial femora and the glenoid portion of a scapula demonstrates that the functional anatomy of Morotopithecus differed markedly from other early and middle Miocene hominoids. Previous studies have consistently associated the vertebral remains with a short, stiff back and with orthograde postures. Although the proximal femur more closely resembles the femora of monkeys than of apes and suggests a moderate degree of hip abduction, the distal femur resembles those of extant large bodied apes and suggests a varied loading regime and an arboreal repertoire that may have included substantial vertical climbing. The femoral shaft displays uniformly thick cortical bone, beyond the range of thickness seen in extant primates, and signifies higher axial loading than is typical of most extant primates. The glenoid fossa is broad and uniformly curved as in extant suspensory primates. Overall, Morotopithecus is reconstructed as an arboreal species that probably relied on forelimb-dominated, deliberate and vertical climbing, suspension and quadrupedalism. Morotopithecus thus marks the first appearance of certain aspects of the modern hominoid body plan by at least 20 Ma. If the suspensory and orthograde adaptations linking Morotopithecus to extant apes are synapomorphies, Morotopithecus may be the only well-documented African Miocene hominoid with a close relationship to living apes and humans.

A hominoid genus from the early Miocene of Uganda.

Fossils from a large-bodied hominoid from early Miocene sediments of Uganda, along with material recovered in the 1960s, show features of the shoulder and vertebral column that are significantly similar to those of living apes and humans. The large-bodied hominoid from Uganda dates to at least 20.6 million years ago and thus represents the oldest known hominoid sharing these derived characters with living apes and humans.

Acid-base regulation in the toad Bufo marinus during environmental hypoxia.

Gas exchange and the correlated changes in blood and tissue metabolic and acid-base status were investigated during long term exposure of the toad Bufo marinus to graded levels of hypoxia. During hypoxia, PCO2 values in blood and tissues fell, leading to a transient alkalosis in the extracellular but not in the intracellular space. A reduction in blood perfusion of the skin during hypoxia may explain why PCO2 was low in sartorius muscle under normoxia, but approached the PCO2 values found in other tissues (gastrocnemius muscle, ventricle) under hypoxia. At PO2 values below the critical PO2, lactate was formed and the decrease in total CO2 was accelerated. Lactate levels in the plasma were higher than in the intracellular space of the skeletal muscles, a finding attributed to the pH-dependent distribution of lactic acid across the cell membrane. The comparison of metabolic proton quantities with those found in the extra- and intracellular acid-base status suggests that CO2 release was accelerated by anaerobic proton formation. The alkalizing effect of decreasing PCO2 in the skeletal musculature was compensated for by a release of base equivalents into the blood. The resulting alkalosis in the blood was probably compensated for by the release of base equivalents into the environment.