Technical note: Quantification of neurocranial shape variation using the shortest paths connecting pairs of anatomical landmarks

Abstract

Three-dimensional geometric morphometric techniques have been widely used in quantitative comparisons of craniofacial morphology in humans and nonhuman primates. However, few anatomical landmarks can actually be defined on the neurocranium. In this study, an alternative method is proposed for defining semi-landmarks on neurocranial surfaces for use in detailed analysis of cranial shape. Specifically, midsagittal, nuchal, and temporal lines were approximated using Bezier curves and equally spaced points along each of the curves were defined as semi-landmarks. The shortest paths connecting pairs of anatomical landmarks as well as semi-landmarks were then calculated in order to represent the surface morphology between landmarks using equally spaced points along the paths. To evaluate the efficacy of this method, the previously outlined technique was used in morphological analysis of sexual dimorphism in modern Japanese crania. The study sample comprised 22 specimens that were used to generate 110 anatomical semi-landmarks, which were used in geometric morphometric analysis. Although variations due to sexual dimorphism in human crania are very small, differences could be identified using the proposed landmark placement, which demonstrated the efficacy of the proposed method.

Dynamics of Learning in Neanderthals and Modern Humans Volume 2

“…One is used as a source model and the other is used as a target model. The semi-landmarks were placed at equally spaced points along the shortest paths between landmarks (Morita et al 2011). The source model has 13 landmarks (anatomical landmarks) and 93 semi-landmarks as shown in Fig.…”

Virtual reconstruction of the Neanderthal Amud 1 cranium

“…Therefore, we defined 62 anatomical landmarks on the external surface of human cranium (Table ). In addition, we approximated the superior nuchal curve between the inion (#3) and the intersection of the superior nuchal line and occipitomastoid suture (#11), the temporal curve between the frontomalare temporale (#8) and stephanion (#9), and the supraorbital curve between the glabella (#2) and frontomalare temporale (#8) using a seventh‐order Bézier curve (Morita et al, ). We then defined 14 additional equally spaced points along the curves, resulting in a total of 76 landmarks.…”

“…Next, we introduced sliding semi‐landmarks (Bookstein, ; Gunz et al, ; Perez et al, ) onto the ovoid ectocranial surface. We defined semi‐landmarks based on the shortest paths between pairs of anatomical landmarks (Morita et al, ) on one modern human specimen (Japanese male, KUMA‐2591, housed at Kyoto University) chosen as a template. Specifically, we used the above non‐sliding landmarks, as well as the 14 equally spaced points along the midsagittal curve between the nasion (#1) and inion (#3), to calculate the shortest paths.…”

Three-dimensional endocranial shape variation in the modern Japanese population

“…In addition, by approximating the curves using a seventh-order Bezier curve (Morita et al, 2013), we calculated the following: (1) 14 equally spaced points along the midsagittal curve between the foramen caecum (#1) and the internal occipital protuberance (#2); (2) 8 equally spaced points (4 on each side) along the anteroinferior border of the anterior cranial fossa between the foramen caecum (#1) and the most lateral point of the posterior border of the lesser wing of sphenoid (#6); and (3) 6 equally spaced points (3 on each side) along the lower border of the sulcus sinus transversi between the internal occipital protuberance (#2) and the intersection of the lower border of the sulcus sinus sigmoidei and transversi (#9). Therefore, in total 44 landmarks were extracted as nonsliding landmarks for each endocranium.…”

“…Based on the shortest paths between pairs of anatomical landmarks (Morita et al, 2013), we defined semi-sliding landmarks on one specimen chosen as a template (Figure 2). Specifically, we calculated the shortest paths connecting pairs of non-sliding landmarks.…”