Temporal Fossa Size

This character is used to measure independently the relative degree of temporalis development, regardless of parietal/temporal bone size. It is distinct from sagittal crest development, which will be correlated directly with the size of these bones, relative to muscle development. For example, a small cranium with moderate to strong temporalis development (e.g., species of P. robustus) will require the formation of a temporal crest to help expand the attachment space requirements of the temporalis. A similar sized muscle in another hominid with increased cranial expansion (and thus increased parietal and temporal bones) will not need a sagittal crest. Because this character is likely to be of importance in terms of sexual dimorphism, only male specimens were examined where possible. In a few cases, however, only female fossil hominins could be used, due to problems of preservation (see later).

This character is defined using the same process as outlined earlier for supraorbital torus thickness (character 2). The index used here is temporal fossa size (area) divided by orbital size (area). An intermediate range is defined by 0.85-1.73 (mean of the four extant hominid species of 1.29 [n = 96] and standard deviation of 0.44). A large fossa is defined by an index greater than 1.73, and a small fossa is defined by an index less than 0.85. All data of extant specimens is taken from originals (unpublished data from DWC), while all data from fossil hominins has been taken from casts housed at the School of Archaeology and Anthropology, the Australian National University.

Males of Gorilla (mean = 1.90 [n = 13]), Pongo (mean = 1.75 [n = 7]), P walkeri (KNM-WT 17000 = 1.77), and P boisei (OH 5 = 1.81) are all defined by a large temporal fossa (= 0). Males of Pan (mean = 1.26 [n = 27]), Australopithecus (Sts 5 = 1.12 [female?]), P robustus (SK 48 = 1.35), H. habilis (KNM-ER 1813 = 1.11 [female?]), and H. ergaster with a mean of 1.06 (n = 2) are all defined by the intermediate condition (= 1). While the sexing of some of the fossil hominins remains problematic, even accepting that some may represent females, they are still well within the intermediate range of the extant hominids. The fossa in H. sapiens has an average of just 0.76 (n = 8), which is small (= 2).

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