Growth in the mandibles of African apes

Growth in the mandibles ofPan troglodytesandGorilla gorillawas examined by use of the line skeleton, a median axis technique for the analysis of complex shapes. Developmental changes in the corpus, ramus, gonial angle, coronoid and condylar processes were assessed to test the hypothesis thatGorillajaws are ontogenetically scaled variants of mandibular morphology inPan. Despite previous observations that aspects of facial morphology related to mastication are ontogenetically scaled in chimpanzees and gorillas, growth of the mandible in African apes does not rigidly adhere to such a pattern. Analysis of line skeletons suggests that growth in different regions of the mandible is decoupled to a significant degree, despite the fact that the spatial relationships between component parts (e.g., ramus and corpus) are established early in ontogeny and remain invariant during growth. Growth in the corpus appears to be strongly influenced by spatial requirements for housing the developing dentition, whereas those regions associated with masticatory muscle attachment appear to be developmentally relatively plastic. These findings support the hypothesis that growth of skeletal tissues is at least partially modulated by the “functional matrix” within which a morphological unit develops (Moss, 1960, 1968).