On aspects of skull form in African apes and orangutans, with implications for hominoid evolution

Abstract

The study of hominoid phylogeny is currently in a state of controversy and debate due to the discovery of new fossil material and reanalysis of the morphology of extant apes. An important key to the resolution of these debates lies in attaining a fuller understanding of the morphological differences in skull form between the African and Asian great apes. In this paper I have analyzed aspects of facial morphology and internal cranial anatomy in the great apes. Results from this study and previous ones suggest that Pongo is characterized by a marked dorsal deflection of the face relative to the basicranium. Many aspects of circumorbital, midfacial, palatal, and mandibular morphology in Pongo may be related to this airorynchous condition. This hypothesis is supported by Enlow's work on form and pattern in the primate and mammalian skull. The position of the face in known Sivapithecus appears to be similar to that seen in Pongo. Although Pongo may be specialized in its marked degree of airorynchy, it seems likely that an important derived feature linking African apes and hominids is a ventral rotation of the splanchnocranium on the neurocranium. The appearance of marked supraorbital tori and ethmofrontal sinuses are probably correlated developments. Additional implications of this work for debates about hominoid phylogeny are discussed.

How and why humans grow thin skulls: Experimental evidence for systemic cortical robusticity

“…The browridge is, thus, more likely to be a developmental consequence of the spatial separation of the splanchnocranium and neurocranium (Shea, 1985;Picq and Hylander, 1989;Ravosa, 1988Ravosa, , 1991 than a beam to provide resistance against twisting or bending forces (e.g., Endo, 1966;Greaves, 1985;Russell, 1985). Finally, the hypothesis that systemic hormones are the primary cause of variation in CVT is not rejected but is instead partially supported by this study.…”

Patterns of craniofacial integration in extantHomo,Pan, andGorilla

“…During ontogeny, the face physically is moved away from the neurocranium by soft tissue; it reconnects with the neurocranium at points along basionnasion length (Enlow, 1982). It was hypothesized that facial form is largely dictated by the spatial positioning of the face relative to the braincase (Shea, 1985), and this relationship between facial growth and projection with the region of neurocranial-splanchnocranial hafting may explain the high degree of integration between basion-nasion length and lower facial projection seen in all African hominoids. The robustness of the edge between basion-nasion length and lower facial projection, but not basion-nasion length-facial height, may speak to the influence the cranial base has in overall cranial form (Lieberman et al, 2000b), as both basion-nasion length and lower facial projection incorporate significant aspects of the middle and anterior cranial fossae.…”

Heterochrony and geometric morphometrics: a comparison of cranial growth in Pan paniscus versus Pan troglodytes

“…Many authors (e.g., Shea 1983aShea , 1985Shea , 1989Leigh et al 2003) focus their attention on the simplest case of allometric scaling, the extension or truncation of ontogenetic trajectories in a logarithmic plot of two size variables. The bivariate concept of allometric scaling is a hypothesis that has an alternative, namely a modification of the ancestral allometry (i.e., the trajectories differ).…”