On the classification of C6 (tuberculum sextum) of the mandibular molars
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- Keene, H.J. Hum. Evol. (1994) 9: 231. doi:10.1007/BF02437929
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Cusp six (C6) of the mandibular molars is well-represented in the Hominoid fossil record and occurs with irregular frequency in the various geographic populations of modernHomo as well as in many of the extant non-human primates. The literature reveals considerable controversy and confusion related to C6 anatomic location, definitions and scoring criteria, and a major problem exists in deciding what actually is the “real” or “true” C6, especially relative to variable hypoconulid (C5) expression (i.e., reduction forms and the “divided hypoconulid”). A method is proposed that involves dual 4-point ranking (absent, small, medium, large) and reporting of C5–C6 covariation within a framework of 13 morphological expressivity categories. When applied to 3 different human populations, the method provided a reasonably clear picture of the actual C5 and C6 covariation patterns observed in the mandibular molar dentition. Data obtained from this exercise illustrated that inter- and intrapopulation differences in reported C6 frequencies could be associated with variable scoring criteria as well as with different levels of occlusal attrition and age distribution of the samples.