With aim of investigating the origin of flattened thoracic cage of apes and human, I examine functional relationship between thoracic cage morphology and positional behaviors. Previous studies suggest that not only typical positional behaviors but also body size had affected the morphological specialization of hominoids. To evaluate the scaling effect, a certain augmentation of data sets on sexual dimorphic apes, large-sized Old World monkeys and some mid- to large-bodied mammals were required.
At the Museum of Comparative Zoology, Harvard University, skeletons such as proboscis monkey (Nasalis larvatus) and white-handed gibbon (Hylobates lar) were photographed and measured. The museum houses primate skeletal collections associated with body measurements, such as white-handed gibbons which were collected in 1930s at Doi Inthanon, presently a national park in northern Thailand, or Bornean orangutans (Pongo pygmaeus) and proboscis monkeys. I met Prof. F. Jenkins Jr. who is prominent for his works on animal locomotion with use of X-ray cinematography to get his idea on thoracic morphology. I also got a chance to attend a thesis seminar on evolution of bipedalism of rodents during at the museum and enjoyed some exchange of information with the speaker.
At the department of paleontology, American Museum of Natural History, I could access to specimens of Malagasy subfossil lemurs by courtesy of Prof. E. Delson. There were several suits of large fragmental ribs which are possibly attributable to giant lemurs which are known for the elongated forelimbs like apes. The weak curvature of the rib, however, differs from that of apes nor living lemuroids, but rather resembles to that of certain kind of monkeys or bears whose thoracic cages are dorso-ventrally elongated. The giant lemurs had taken distinctive evolutionary course in the trunk proportion and the forelimb function.
Morphological data of about 70 individuals of great apes, baboons, carnivores, marsupials were collected at Division of Mammals of the following museums as well ; American Museum of Natural History, Smithsonian Museum of Natural History, and the Field Museum of Natural History. Using the captured images of specimens, species mean shape of thoracic cage and the scaling relationship of some morphometrical properties will be analyzed. Through these analyses, unique aspects of morphological evolution of hominoids will be elucidated.