First Records of Talon Cusps on Baboon Maxillary Incisors Argue for Standardizing Terminology and Prompt a Hypothesis of Their Formation

Abstract

Dental characters can provide vital clues for understanding intra-and intertaxonomic morphological variation and its underlying genetic and environmental components. However, the unambiguous identification of particular traits and their comparative study is often confounded by lack of consistent terminology in the relevant literature. This difficulty is exacerbated when the etiologies are not completely understood, as is the case with talon cusps. To date, research on talon cusps has focused on modern humans. In many instances, descriptions of talon cusps appear in clinical case studies focusing on their treatment and removal. What is lacking in those discussions, though, is a comparative framework, in which the occurrence of talon cusps in nonhuman primates, and possibly other mammals, is established and understood. Here, we report on a taloned upper central incisor of a wild baboon (Papio hamadryas ursinus) from South Africa. The anomalous incisor of this individual includes an exaggerated accessory cusp diagnosed as a Type II talon. Microcomputed tomographic and radiographic analyses show that the taloned cusp possesses enamel, dentin, and pulp. In addition, we identified an unclassifiable talon cusp on a central maxillary incisor of a baboon skull housed in the Smithsonian Institution's Natural History Museum collection. Our observations of talon cusps on baboon incisors demonstrate that, with regard to this phenomenon, systematic study of nonhuman primates is much needed, along with a consistent use of terminology in the anatomical and anthropological literature. Finally, we present a hypothesis of the formation of talon cusps on mammalian incisors. Anat

Talon cusp expression in Cayo Santiago rhesus macaques (Macaca mulatta)

“…Overall, this study found that in rhesus monkeys, as in baboons and humans, the talon cusp is a rare trait. In this study, overall prevalence was 9.4% while the single study of baboons reported a lower prevalence of 2.94% (Heaton & Pickering, 2013). The difference in prevalence between the two studies could be a result of thresholds for scoring the talon cusp as present.…”

“…that if males have larger incisors than females, then there would be more space available for additional cusps to form during crown morphogenesis, leading to a greater likelihood of talon cusp formation in males than in females (Heaton & Pickering, 2013). This suggestion is based on the "Patterning Cascade Model" (PCM) of crown morphogenesis (Jernvall & Jung, 2000).…”

“…The difference in prevalence between the two studies could be a result of thresholds for scoring the talon cusp as present. Heaton and Pickering (2013) did not appear to include some of the smaller forms that were included here.…”

“…Finally, Talon 3 cusps, are described as "trace talon[s]" that are "…enlarged or prominent cingula and their variations, i.e., conical, bifid, or tubercle-like." Although Heaton and Pickering (2013) argued that "trace talons" can be conflated with the tuberculum dentale, other researchers have, like Hattab et al (1995), defined talon cusps more broadly, along a continuum ranging from enlarged cingula to full "accessory cusps" (Chawla, 1983;Davis & Brook, 1986;Harris & Owsley, 1991).…”

Coexistence of true talon cusp and double dens invaginatus in a single tooth: a rare case report and review of the literature

“…The etiology of talon cusp is still unknown. Lots of work have been completed on human talon cusps, but a recent article has shown that baboons may also possess cases, as well . Some researchers reported the occurrence of this case in the same family members indicating the genetic influences of this anomaly .…”