On Skull Form and the Supraorbital Torus in Primates

Stressed out: Masticatory forces and primate circumorbital form

“…Moreover, the in vivo analyses, especially work on the primate zygomatic arch (Hylander and Johnson, 1997), demonstrate that gross morphology alone cannot be used to infer levels of masticatory stress and strain. Lastly, we suggest that Bookstein et al's (1999) data on hominoid browridge and frontal sinus proportions further support the hypothesis that ontogenetic and interspecific variation in primate circumorbital form is correlated directly and/or indirectly with variation in cranial size and neural-orbital disjunction (Hylander and Ravosa, 1992;Moss and Young, 1960;Ravosa, 1988Ravosa, , 1991aRavosa et al, 2000a,b;Ross and Hylander, 1996;Shea, 1986;Vinyard, 1994;Vinyard and Smith, 1997).…”

“…Second, we indicate that recent in vivo bone-strain analyses provide no support for any masticatory-stress hypothesis of circumorbital form. Third, based on experimental and morphological data, we show that, rather than being adapted to counter masticatory stresses, variation in browridge proportions and frontal sinus pneumatization is supportive of the spatial model of supraorbital torus formation (Moss and Young, 1960;Shea, 1986;Ravosa, 1988Ravosa, , 1991aHylander and Ravosa, 1992).…”

“…7: p. 223) are adaptations to resist masticatory loads, then why do orangutans, large-bodied apes with a very hard/tough diet, exhibit such diminutive browridges? We believe the answer to this question is that ontogenetic and interspecific variation in the position of the orbital apertures relative to the anterior cranial vault underlies the extent of anthropoid browridge formation (Moss and Young, 1960;Ravosa, 1988Ravosa, , 1991aShea, 1986).…”

Strain in the Galago facial skull

“…It is thus interesting that a large component of the variation in primate circumorbital robusticity is correlated directly and/or indirectly with variation in overall skull size and that postorbital bar and supraorbital torus dimensions scale positively in interspecific and ontogenetic comparisons (Moss and Young, 1960;Shea, 1986;Ravosa, 1988Ravosa, , 1991a Hylander and Ravosa, 1992;Vinyard, 1994;Vinyard and Smith, 1997). Indeed, the presence of higher circumorbital safety factors for masticatory loads in larger forms may be related to the fact that larger sister taxa and larger dimorphic males exhibit more robust circumorbital structures (Ravosa, 1988(Ravosa, , 1991a.…”

Statistical estimators of frontal sinus cross section ontogeny from very noisy data

“…The leading explanations of their functional role in archaic Homo are the spatial models of supraorbital torus formation (Moss and Young, 1960;Shea, 1986;Hylander et al, 1991;Ravosa, 1991) and the masticatory stress hypothesis models (Demes, 1982(Demes, , 1987Spencer and Demes, 1993;Bookstein et al, 1999;Prossinger et al, 2000a).…”