Articular Tubercle Height

This is defined by the perpendicular distance between the tip of the articular tubercle and the plane of the zygomatic arch, divided by the cranial base geometric mean, which is calculated as a geometric mean of four chords (basion-opisthion, basion-sphenobasion, bi-entoglenoid, and bi-cartoid canal [see Strait, 2001]). This index defines the relative development of the articular tubercle, which is related to the requirements of the outer oblique bands of the temporomandibular ligament, which converge onto an area at the back of the neck of the mandibular condyle. This ligament helps keep the condyle, disc, and temporal bone firmly opposed (Aiello & Dean, 1990). As such, it is an important functional component of the TMJ. The character definitions and allocations to hominin taxa have been taken directly from Strait (2001).

The primitive character state is for a moderate to large tubercle, as seen in Pongo, Gorilla, Pan, Praeanthropus, Australopithecus, P. walkeri, P. robustus, and P boisei ( = 0). The condition in H. habilis is said to be variable (= 1), while in K. rudolfensis, H. ergaster, and H. sapiens, it is undeveloped (= 2) (see Strait, 2001). While preservation means that a value cannot be generated for Ardipithecus or members of the "anamensis group", it is described as undeveloped in both taxa and is coded as small (see T.D. White et al., 1994; M.G. Leakey et al., 1995).

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