ABSTRACT
Morphologically, pygmy chimpanzees are more 'generalized' in body size, body build and sexual dimorphism than the common species and may provide a better prototype for studying the derivation of the earliest hominids and African apes. Pygmy chimpanzees on the average weigh less than the average common chimpanzee, but with much overlap: 25–48 kg, compared to 25–60 kg or somewhat more. Pygmy chimpanzees have smaller facial and canine dimensions, smaller average cranial capacities, and the two species can be discriminated on mandibular length alone. Pygmy chimpanzees have a narrower trunk and more gracile upper body, as reflected in significantly smaller clavicular length, scapular dimensions and iliac and sacral breadths. As to sexual dimorphism, pygmy chimpanzees are moderately sexually dimorphic in body weight, but no dimorphism can be detected in cranial capacity, limb bone lengths or robusticity, or in anterior and posterior dentition. Laboratory and field studies reveal pygmy chimpanzees as highly intelligent and flexible in feeding, locomotor, sexual and communicatory behavior.
