Lingual Cuspule and Paraconid, on One Archaic Period Modern Human from the Ohio Valley

Over the course of human evolution there is a simplification in the expression of tooth traits (i.e. a reduction in cusp number, and occlusal ridges; Bailey and Hublin, 2013); however, there still exists considerable variation in the expression of dental morphology in world populations (Turner et al., 1991; Scott and Turner, 1997; Hanihara, 2008; Scott et al., 2016; Irish, 2016). Placement of tooth cusps, both principal and accessory, can be used to discuss morphological variation. Generally, accessory cusps are initiated after the principal cusps have formed (Kraus and Jordan, 1965; Hillson 1996) making their expression more variable and less frequent than principal cusps. While many mandibular paramolar structures, such as the Mandibular Molar Pit -Tubercle (MMTP; Weets, 2009) and protostylid (Dahlberg, 1950), have been identified and described in several populations, there are several traits that are less common. For example, odontomes on premolars, the mesial canine ridge (Scott and Turner, 1997), and the labial talon cusp on incisors (Stojanowski and Johnson, 2011) are much less common traits within a given population. Traits that are found in 4-7% of a population are considered “rare”; “very rare” traits are found in 1 3% of a population, and “near absent” when they are found in less than 1% of a population (Scott and Turner 1997: 191, 193). Assessing patterns of dental trait expressions are useful to understand biological variation, migration of modern human populations around the world (Scott and Turner, 1997; Hanihara, 2013; Scott et al., 2018), and evolutionary changes within and between hominin taxa (Bailey and Hublin, 2013; Martinon-Torres et al., 2013; Guatelli-Steinberg 2016). The goals of this paper are to 1) describe two rare lower molar traits, the lingual cuspule (Irish, 1991) and the paraconid, and 2) contextualize them in modern human variation. Only one other study has identified the lingual cuspule, which was observed on a single individual (Irish, 1991). The paraconid is a principle cusp which has been identified in early primate ancestors, but appears to have been lost, with the exception of tarsiers, before the emergence of hominins (Gregory, 1922; Ankel-Simons, 2007; Fleagle, 2013). To date, no studies have reported this cusp in modern humans. Both the lingual cuspule and the paraconid were observed on mandibular third molars of a single individual from the Archaic period (2500-500 BC) in the Ohio Valley. Neither of these dental anomalies has been extensively documented in modern humans, and both may be considered near absent in world populations. It is possible that these molar cusps are simply overABSTRACT Dental anomalies in modern humans are used to discuss biological variation and evolutionary changes. Presented here are the lingual cuspule and paraconid; two traits considered near absent (occurring <1%) in world populations. The only other example of a lingual cuspule comes from an African population. The paraconid was thought to have been lost in primate evolution starting in the Oligocene (34-23 MYA). Both traits were found on the lower third molars of a male individual from the late Archaic (2500-500 BC) site of Shick in Handcock County, Ohio. Here the lingual cuspule is present unilaterally on the right third molar, whereas the other reported case shows the trait being expressed bilaterally on the first molars. Therefore, the lingual cuspule can be found on molars across the row. Additionally, each example exhibits a fully developed cuspule with a free apex. These data indicate the lingual cuspule could be incorporated into studies of biodistance and morphological variation. Contextualizing the paraconid is more challenging given that the only reported examples of this trait in extant primates come from the tarsier. The expression of a paraconid in modern humans could suggest secondary evolution of this trait. Further reporting of both the lingual cuspule and paraconid are necessary to better understand these traits and discuss their importance in modern human variation.