Premolar Root and Canal Variation in Extant Non-Human Hominoidea N. Collin Moore, 1 * Jean-Jacques Hublin, 1 and Matthew M. Skinner 2,1 1 Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Germany 2 School of Anthropology and Conservation, University of Kent, UK KEY WORDS premolar; root; canal; hominoid; Pan; Gorilla; Pongo; Hylobates; cervical size; dental anatomy; taxonomy ABSTRACT Objectives: The premolar sub-cervical region in four non-human extant ape genera are exam- ined to: 1) define a classification scheme for the premo- lar root system in order to rigorously characterize, quantify and document variation in root and canal, form, number and configuration; 2) compare this varia- tion within and between genera; and 3) test the hypothe- ses that sex and size (i.e., the “size/number continuum,” Shields, 2005) of the premolar are determinants of root/ canal form and/or number. Materials and Methods: Microtomography and 3D visu- alization software are utilized to examine a large sample of Hylobates, Pan, Gorilla, and Pongo (n 5 951 teeth). Each premolar root system is examined to ascertain the expected level of variability for each taxon. Cervical sur- face area (mm 2 ) serves as a metric proxy for tooth size. A Chi-square test of independence is used to assess for variability differences between and within each taxon, and Mann–Whitney U tests are employed to assess the predicted relationship between tooth size and variation within each taxon. Results: Our findings indicate that root and canal config- urations, non-metric root traits and tooth size can distin- guish between extant ape genera. Within the four ape taxa, premolar size variation is generally, but not always, correlated with canal/root number. Our results indicate that males and females within genera differ in tooth size but not in canal/root form and number. Discussion: We report previously undocumented varia- tion in the study taxa. Our results are discussed within the context of Miocene Apes as well as the developmen- tal and systematic implications. Am J Phys Anthropol 158:209–226, 2015. V C 2015 Wiley Periodicals, Inc. Premolar root structure in extant apes and fossil hom- inoids and hominins can vary in root and canal number, form, and size. This variation has been the subject of considerable study and has been examined with respect to tooth development and function, sexual dimorphism, and taxonomic and phylogenetic hypotheses within Hominoidea (Sperber, 1974; Abbott, 1984; Wood et al., 1988; Wood and Engleman, 1988; Tobias, 1995; Brunet et al., 1996; Kupczik et al., 2005; Shields, 2005; Emonet et al., 2012, 2014; Hamon et al., 2012; Rossie and MacLatchy, 2013; Emonet and Kullmer, 2014). Given its variation within the human evolutionary tree, premolar root structure has also been implicated in the system- atics of fossil hominins (Sperber, 1974; Abbott, 1984; Wood et al., 1988; Zilberman and Smith, 1992; Tobias, 1995; Brunet et al., 1996; Berm udez de Castro et al., 1999; Shields, 2005; Kupczik and Dean, 2008; Emonet, 2009; Emonet et al., 2012; Prado-Sim on et al., 2012). However, due to limitations in imaging fine details (i.e., premolar root and canal number and position) of teeth within jaws, an adequate characterization of variation has not been published for extant non-human hominoids. In this contribution, we report on the relationship between variation in premolar root/canal morphology in a large sample of Hylobates, Pongo, Gorilla, and Pan, exam- ine correlations with tooth size and sex, and in doing so elucidate the developmental processes underlying root growth and the evolution of premolar root morphology in the hominoid clade (including fossil hominins). Based primarily on the study of extant apes, Emonet and Kullmer (2014) and several previous studies (e.g., Abbott, 1984; Wood et al., 1988; Wood and Engleman, 1988; Kupczik et al., 2005) have inferred the ancestral hominoid pattern of premolar tooth roots. In Pongo, Gorilla, and Pan, the typical pattern for the maxillary third (UP3) and fourth (UP4) premolars is two elliptical buccal roots and one elliptical lingual root (each root having a single canal). The mandibular third premolar (LP3) typically has one elliptical mesio-buccal root (with one canal) and one plate-like distal root (with two circu- lar canals). The mandibular fourth premolar (LP4) typi- cally has a plate-like mesial and distal root (each having two circular canals). Although not the focus of this study, modern humans (as well as many species in the genus Homo) tend to exhibit a derived condition of reduced root number in the form of single and some- times double rooted maxillary and mandibular premo- lars; however, ethnogeographical variation has been documented (Turner, 1981; Abbott, 1984; Chaparro et al., 1999; Sert and Bayirli, 2004; Shields, 2005). In contrast, the second derived condition manifests as two elaborated or “molariform” mandibular premolar roots Grant sponsor: Max Planck Society. *Correspondence to: N. Collin Moore, Department of Human Evolution, MPI-EVA Deutscher Platz 6, Leipzig, Germany 04103. E-mail: collin_moore@eva.mpg.de Received 26 May 2014; revised 11 May 2015; accepted 14 May 2015 DOI: 10.1002/ajpa.22776 Published online 11 August 2015 in Wiley Online Library (wileyonlinelibrary.com). Ó 2015 WILEY PERIODICALS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 158:209–226 (2015)