Body Size and Skeletal Allometry in African Apes

Abstract

The African apes represent a group of closely related primate taxa that differ substantially in adult body size. The close phylogenetic affinity of pygmy chimpanzees (Pan paniscus), common chimpanzees (Pan troglodytes), and gorillas (Gorilla gorilla) is affirmed by both molecular and morphological data. Most biomolecular studies to date, however, have been unable to resolve the chimpanzee-gorilla-human trichotomy into a definitive chimpanzee-gorilla clade that would have humans as a sister group (e.g., Sarich, 1968, and this volume; Zihlman et al., 1978; Bruce and Ayala, 1979; Goodman, 1982). The evolutionary tree for humans and pongids based on cleavage maps of mitochondrial DNA (Ferris et al., 1981; Templeton, 1983) is a notable exception in this regard; these data first group pygmy and common chimpanzees into a phyletic unit that is linked next to gorillas. Humans are then joined to the African ape clade before the orangutan (Pongo pygmaeus). A variety of shared, unique features of the karyotypes of African apes lend strong credence to this phylogeny (Mai, 1983). Morphological analyses of the teeth and locomotor skeletons of pongids and humans [summarized in Ciochon (1983)] also corroborate the Ferris et al. branching sequence.