The timing of spheno‐occipital fusion in hominoids

Abstract

The degree of spheno-occipital fusion has been used to assign a relative age to dentally mature hominoid cranial specimens. However, a recent study of captive individuals (Poe: Am J Phys Anthropol 144 (2011) 162–165) concluded that fusion of the spheno-occipital suture in great ape taxa is of little utility for aging dentally mature individuals. In this contribution, I use dentally mature samples of extant hominoid taxa (Homo sapiens, Pan troglodytes schweinfurthii, Gorilla gorilla gorilla, Pongo pygmaeus pygmaeus and Hylobates lar) to investigate a) the temporal relationship between spheno-occipital fusion and dental maturity, b) whether there is an association between the degree of spheno-occipital fusion and relative age, c) whether there are differences in relative timing of spheno-occipital fusion between taxa, and d) whether there are sex differences in the relative timing of spheno-occipital fusion. Results suggest that a) a substantial proportion of dentally mature wild-shot chimpanzee, gorilla and orang-utans have unfused or partially fused spheno-occipital synchondoses, b) there is an association between the degree of spheno-occipital fusion and age, c) there are interspecific differences in the timing of spheno-occipital fusion, and d) there are significant sex differences in spheno-occipital fusion in chimpanzees, orang-utans and gibbons. Thus, contrary to previous work, degree of spheno-occipital fusion is a potentially useful indicator of relative maturity, especially in great ape taxa.

Sagittal crest formation in great apes and gibbons

“…Among the taxa investigated in this study, males show a higher frequency of sagittal cresting than do females. These results are consistent with patterns of cranial growth beyond dental maturity and with spheno-occipital fusion being delayed in gorillas and orangutans (Randall, 1943;R€ ohrer-Ertl, 1988;Leutenegger & Masterson, 1989a,b;Masterson & Leutenegger, 1990Uchida, 1996;Hens, 2003Hens, , 2005Balolia et al 2013;Gordon et al 2013;Balolia, 2015).…”

“…; Gordon et al. ; Balolia, ), in conjunction with the need to increase muscle attachment area, have important applications for reconstructing the social behaviour of extinct primate taxa. In particular, if the timing of sagittal crest development in males is associated with a male reproductive strategy characterised by intense intrasexual competition across primates, examination of sagittal crest emergence and associated scaling relationships in fossil assemblages may allow us to begin to reconstruct the nature of intrasexual male competition in those extinct hominin taxa that display evidence of a sagittal crest.…”

“…Finally, an understanding of the biological basis of sagittal crest development related to the timing of other indicators of maturity (e.g. Shea, 1986Shea, , 1988R€ ohrer-Ertl, 1988;Leutenegger & Masterson, 1989a,b;Masterson & Leutenegger, 1990Uchida, 1996;Hens, 2003Hens, , 2005Balolia et al 2013;Gordon et al 2013;Balolia, 2015), in conjunction with the need to increase muscle attachment area, have important applications for reconstructing the social behaviour of extinct primate taxa. In particular, if the timing of sagittal crest development in males is associated with a male reproductive strategy characterised by intense intrasexual competition across primates, examination of sagittal crest emergence and associated scaling relationships in fossil assemblages may allow us to begin to reconstruct the nature of intrasexual male competition in those extinct hominin taxa that display evidence of a sagittal crest.…”

Allometry and advancing age significantly structure craniofacial variation in adult female baboons

“…; Zihlman et al. ; Poe, ; Franklin & Flavel, ; Balolia, ). As it is assumed that processes of skeletal maturation largely function the same in the craniofacial skeleton (CFS) and long bones (e.g.…”

“…Fusion of the spheno-occipital synchondrosis and eruption of the third molars are traditionally accepted as the craniofacial features in humans and non-human primates that define an individual as being an 'adult' (e.g. Bramblett, 1969;Falk et al 1989;Wang et al 2006;Zihlman et al 2007;Poe, 2011;Franklin & Flavel, 2014;Balolia, 2015). As it is assumed that processes of skeletal maturation largely function the same in the craniofacial skeleton (CFS) and long bones (e.g.…”