Geometric morphometric analysis of the intermediate phalanx of Ouranopithecus macedoniensis—a pilot study

Abstract

Ravin de la Pluie (RPl) in the Axios valley, Greece, is one of the three localities where the material of the Late Miocene ape Ouranopithecus macedoniensis has been found to date (de Bonis et al., 1974; de Bonis and Melentis, 1978; Koufos and de Bonis, 2006; Koufos et al., 2016). The material from RPl is rich; it includes maxillary and mandibular remains, multiple isolated teeth, and just a few postcranial specimens, which to date represent the only postcranial remains associated with this species: two phalanges (proximal: RPl-86, intermediate: RPl-87). A first analysis of the phalanges was conducted in 2014 (de Bonis and Koufos, 2014). In that study, de Bonis and Koufos followed a comparative approach, using multivariate analyses of linear measurements to assess morphological similarities to extant and fossil primates. De Bonis and Koufos concluded that both phalanges likely belong to the hand, but that an allocation to the foot cannot be excluded due to the lack of comparative material from the same species. However, since the phalanges are the only postcranial remains associated with this species so far, identifying them as either manual or pedal phalanges, as well as allocating them to a ray, is crucial. Having this information would allow for further, more detailed examinations, such as more accurate comparative analyses and reconstruction of locomotor behavior. Therefore, the goal of this study is to contribute to the identification of the intermediate phalanx RPl-87 through the application of three-dimensional (3D) geometric morphometrics (GM). Geometric morphometrics is a statistical analysis of form (shape and size) in which, in contrast to traditional morphometrics, geometric information of the investigated structures can be retained throughout the analysis to provide a more detailed evaluation of shape differences (Slice, 2007). By comparing the shape of the better-preserved phalanx RPl-87 with manual and pedal intermediate phalanges of extant primates, we aim to address the following research questions: 1. Does RPl-87 belong to the foot or the hand? 2. What ray can RPl-87 be assigned to? 3. Does the specimen show morphological affinities to extant primates?