Abstract:
Ouranopithecus macedoniensis from Greece belongs to the hominoids that flourished during the Miocene epoch (~23-6 Ma) in Africa and Eurasia. The hominoids are our distant relatives, and their emergence represents the beginning of the long path that led to humans. Although their appearance was plentiful, their fossil record is fragmentary and scarce.
This dissertation aims to reconstruct and analyze fragmentary fossil specimens belonging to O. macedoniensis and explore craniodental similarities (or dissimilarities) between this Miocene ape and primarily extant great apes. Research questions addressed in this dissertation include: (1) What are the morphological affinities of the reconstructed facial area of O. macedoniensis in relation to the extant great apes?, (2) Does male-female mandibular shape vary within O. macedoniensis?, (3) How do mandibular shape, size, and sexual dimorphism in O. macedoniensis compare to the extant great apes?, and (4) Is the study of the internal root morphology the key to resolving the debatable phylogenetic position of O. macedoniensis?. These research questions are explored by applying virtual techniques and utilizing advanced statistical analyses.
Study 1 presents the virtual reconstruction of the facial anatomy of O. macedoniensis, that of the XIR-1 cranium and RPl-128 maxilla; the only cranial fossils found heretofore belonging to this species. This study aimed to quantify, using advanced geometric morphometrics, shape variation between the virtual reconstructions of O. macedoniensis and a comparative sample of other fossil hominoids, extant great apes (Gorilla, Pan, and Pongo), and humans. The results showed that O. macedoniensis groups phenetically with Gorilla, rather than Pan, Pongo, or Homo. In the principal component analyses, O. macedoniensis falls within or close to the Gorilla convex hull. Both specimens, face and maxilla, are classified as Gorilla based on discriminant function analyses.
Study 2 presents the 3D analysis of four partial mandibles (RPl-54; 56; 75; 79) and a ramus (RPl-391) belonging to O. macedoniensis. This study aimed to explore mandibular shape similarities between O. macedoniensis and a comparative sample of extant great apes and assess mandibular shape variation and homogeneity within O. macedoniensis. Additionally, the degree of mandibular sexual dimorphism was explored in O. macedoniensis and compared to that of extant great apes. The results indicated that mandibular shape could differentiate O. macedoniensis from the extant great apes, although it showed some shape similarities to the larger great apes (Gorilla and Pongo). The PCA results suggested that the male and female specimens of O. macedoniensis have mandibular shapes that are quite similar. The analyses of the Procrustes distances suggested, however, that there is more shape variation in O. macedoniensis than in the extant great apes. Moreover, the degree of sexual dimorphism in O. macedoniensis was found to be greater than in any of the great apes.
Study 3 is a case study and presents a 3D analysis of the mandibular dentition of O. macedoniensis. Two mandibular fragments (RPl-54 and 75) and an isolated lower molar (RPl-237) from this species are studied and compared with the literature. This study aims to observe and characterize the root morphology and length in the lower post-canine dentition of O. macedoniensis, and compare it to extant and extinct taxa (including Graecopithecus freybergi). The results showed that the lower dentition of the two mandibular specimens used exhibits a similar mandibular root morphology to each other, implying homogeneity in this species. O. macedoniensis shares several dental traits with the African great apes and Pongo. However, the results did not indicate a clear relationship of O. macedoniensis with any of the great apes in particular. Additionally, the results showed that O. macedoniensis differs from G. freybergi in the root and pulp canal configuration. This supports the hypothesis that O. macedoniensis is taxonomically distinct from G. freybergi.
This dissertation emphasizes the importance of applying advanced techniques in the investigation of the fragmentary fossil record. It also highlights the need for unity among people working on Miocene materials, providing more robust comparative analyses and offering more decisive findings on very debated specimens.
Hominoid evolution