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International audience; Rudapithecus is a hominid known from the 10 Ma site of Rudabánya, in Hungary, sharing features that are unique to the African ape and human clade. However, the taxonomic diversity within Rudapithecus and its phylogenetic relationships with other fossil and extant hominid taxa remain controversial. We used X-ray microtomographic imaging to characterize the endostructure of Rudapithecus lower molars and compared it with that of other European Miocene apes (Dryopithecus and Ouranopithecus), the South Asian Miocene ape Sivapithecus, and extant hominids. We assessed 3D tooth crown tissue proportions, enamel thickness distribution patterns and conducted geometric morphometric analyses of the enamel-dentine junction (EDJ). Rudapithecus has moderately thick enamel similar to Pongo, thicker than in Dryopithecus and extant African apes, but thinner than in Ouranopithecus and extant humans. The thickest enamel is found at the apex of the cusps, similar to Gorilla, while in the other extant hominids it is located more laterally along the cusps. In EDJ morphology the Miocene apes overlap with Pongo but not extant hominines. Among Miocene apes only, Rudapithecus, Dryopithecus and Ouranopithecus plot close to one another and are discriminated from Sivapithecus, consistent with previous analyses indicating that the European taxa form a clade. RUD 14 plots closest to Ouranopithecus and closer to Dryopithecus than to RUD 212. The difference between the two Rudabánya specimens is greater than the difference between Rudapithecus and Dryopithecus, which is consistent with previous observations suggesting the presence of more than one ape taxon at Rudabánya.

The internal structure of the bones and teeth of extinct primates holds a significant amount of valuable paleobiological information for assessing taxonomy, phylogenetic relationships, functional, dietary and ecological adaptive strategies, and reconstructing overall evolutionary history. Technologies based on X-ray microfocus (X-mu CT) and synchrotron radiation (SR-mu CT) microtomography are increasingly used to non-invasively and non-destructively investigate the endostructural properties of fossil mineralized tissues. However, depending on the taphonomic dynamics that affected the specimens following deposition, and on the nature of diagenetic processes, X-mu CT and even SR-mu CT may provide only faint or no contrast between the mineralized tissues, thus complicating or inhibiting the study of structural features. Using a diverse sample of dentognathic hominid specimens from continental Asia, East Africa and Indonesia, chronologically ranging from the Late Miocene to the Early Middle Pleistocene, we present examples of the successful application of another imaging technology, neutron microtomography (n-mu CT), for the extraction, 3D rendering and quantitative assessment of internal morphological detail. The specimens were scanned at the ANTARES Imaging facility (SR4a beamline) at the FRM II reactor of the Technical University of Munich, Germany, at energies ranging from 3 to 25 meV. The datasets were reconstructed with a voxel size from 20 to 27 mu m, i.e., at resolutions directly comparable to the X-ray-based microtomographic records commonly used in paleobiological studies of fossil primate remains. Our analyses focused on a mandible, SNSB-BSPG 1939 X 4, representing the Late Miocene hominid Sivapithecus from the Siwaliks of Pakistan; the early Pleistocene (Gelasian) partial mandible HCRP-U18-501 from Malawi, among the earliest specimens attributed to the genus Homo; and an assemblage of hominid dentognathic specimens from the Early Middle Pleistocene deposits of the Sangiran Dome, Indonesia. While X-ray-based imaging revealed from low to moderate internal contrasts for the specimen of Sivapithecus, or from extremely poor to virtually no contrast for the Pleistocene remains from East Africa and Indonesia, the application of n-mu CT produced sufficient differences in contrast to distinguish between tooth tissues on the one hand, and between cortical and trabecular bone on the other, thus enabling reliable qualitative and quantitative assessments of their characteristics.