ancestors) and Panina (chimpanzees) separated about to . Evolution of the pelvis In primates, the pelvis consists of four parts—the left and the right hip bones which meet in the mid-line ventrally and are fixed to the sacrum dorsally and the coccyx. Each hip bone consists of three components, the ilium, the ischium, and the pubis, and at the time of sexual maturity these bones become fused together, though there is never any movement between them. In humans, the ventral joint of the pubic bones is closed. The most striking feature of evolution of the pelvis in primates is the widening and the shortening of the blade called the ilium. Because of the stresses involved in bipedal locomotion, the muscles of the thigh move the thigh forward and backward, providing the power for bi-pedal and quadrupedal locomotion. See also Evolution of mammals List of fossil primates Primate#Evolution Timeline of human evolution References Bibliography Further reading Van Schaik, Carel P., and Peter M. Kappeler. "The evolution of social monogamy in primates". Monogamy: mating strategies and partnerships in birds, humans and other mammals. Cambridge University Press, Cambridge (2003): 59–80. External links The First Primates at anthro.palomar.edu