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The hominoid cranium represents a tightly constrained, functionally and developmentally integrated structure subject to multiple selective influences. Modern apes are the remnant of a much more diverse radiation, raising issues about their suitability as models for earlier hominoids. Among gibbons the folivorous siamang is cranially distinctive. The markedly airorynchous Pongo is cranially highly variable and lacks the anterior digastric muscle, thereby contrasting with other hominoids (except Khoratpithecus). African apes share a common cranial pattern differentiated by varying growth rates, not duration. Airorhynchy is common among fossil hominoids and differentiates hominoids from non-hominoids, suggesting that African ape klinorhynchy is derived. Bonobos are cranially smaller, lighter, and less dimorphic than chimpanzees. These are comparatively uniform, with extensive overlap between subspecies, whereas gorillas display considerable contrasts, especially between east and west populations. Early Miocene hominoids are already cranially diverse, with most species probably soft- or hard-fruit feeders. Middle and Late Miocene forms from Africa, Europe, and Western Asia are thicker enameled with more strongly constructed crania suggesting harder diets, although Dryopithecus (soft frugivory) and Oreopithecus (folivory) are exceptions. South and East Asian fossil hominoid diets ranged from soft fruits through harder items to bulky, fibrous vegetation. All extant ape crania are relatively lightly constructed compared with fossil forms, again prompting questions about their suitability as adaptive models of earlier hominoids.

DOI: 10.1007/978-3-642-39979-4_35

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