Human Evolution

, Volume 9, Issue 3, pp 231-247

First online:

On the classification of C6 (tuberculum sextum) of the mandibular molars

  • H. J. KeeneAffiliated withScience Center Dental Branch Department of Oral Diagnostic Sciences, The University of Texas Health

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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.

Key words

Cusp six lower molars dental morphology taxonomy