Sexual dimorphism in the zygomatic and zygomatic arch: Using geometric morphometrics on a Dutch population, Middenbeemster from 1829-1866

In this thesis, the size and shape differences between male and female zygomatic bones and zygomatic arches are examined in order to better understand and improve the macroscopic sex estimation methods that are currently used for these regions. These regions are used in macroscopic osteological methods of sex estimation but the exact nature of the differences is poorly understood: Is it a difference in shape, in size, or both, and where are the differences located exactly? In osteological methods, it is thought that the male zygomatic is more square in shape with a larger marginal tubercle than in females. For the zygomatic arch, the male arch is said to be thicker than that of females. For the orbit, the male orbit is purportedly more square and the female orbit more round. This thesis uses three dimensional (3D) models and geometric morphometrics to investigate sexual dimorphism of the zygomatic and zygomatic arch. Geometric morphometrics is a method that uses images, in this case...Show moreIn this thesis, the size and shape differences between male and female zygomatic bones and zygomatic arches are examined in order to better understand and improve the macroscopic sex estimation methods that are currently used for these regions. These regions are used in macroscopic osteological methods of sex estimation but the exact nature of the differences is poorly understood: Is it a difference in shape, in size, or both, and where are the differences located exactly? In osteological methods, it is thought that the male zygomatic is more square in shape with a larger marginal tubercle than in females. For the zygomatic arch, the male arch is said to be thicker than that of females. For the orbit, the male orbit is purportedly more square and the female orbit more round. This thesis uses three dimensional (3D) models and geometric morphometrics to investigate sexual dimorphism of the zygomatic and zygomatic arch. Geometric morphometrics is a method that uses images, in this case 3D scans of crania. On the images, landmarks are indicated. Four sets of landmarks are examined in this thesis: All landmarks together, landmarks on the zygomatic, landmarks on the zygomatic arch, and landmarks on the orbits. These landmarks are then analyzed with a general procrustes analysis, which removes rotation, location, and size. This means that only shape remains. Two different principal component analyses (PCA) follow. The first is a normal PCA, while the second includes size to examine the form (shape with size). Differences are looked for in size, shape, and form. Because shape can change with size (allometry) the occurrence of this is also examined. The material that is analyzed is 65 crania (29 females and 36 males) from the Middenbeemster cemetery in the Netherlands, mostly from the 19th century. The results show differences between males and females in size and in form, but no clear difference in shape. Allometry is present in the zygomatic, the zygomatic arch, and orbits, but only in the orbits does allometry explain more than 10% of the change in shape. The allometry in the orbits corresponds to the differences noted by the macroscopic method mentioned above. All the differences between males and females come from a difference in size. Only for the zygomatic arch, does form work better than size in differentiating the sexes. Differences in shape do not clearly differentiate between males and females. The accuracy for the size differences for all the landmarks and the zygomatic are both 83%. The form of the zygomatic arch also has an accuracy of 83%. This thesis has contributed to our knowledge about the location of differences between males and females for the zygomatic bone, zygomatic arch and orbits. The differences are mainly in size, and for the zygomatic arch in both size and shape (form). With this knowledge we can improve upon the macroscopic methods for sex estimation.Show less

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Sexual dimorphism in the zygomatic and zygomatic arch: Using geometric morphometrics on a Dutch population, Middenbeemster from 1829-1866