Technical Summary ![](https://hominid.la.psu.edu/files/2019/05/RtArrowicon.gif)
Quantitative Morphology
Quantitative morphology refers to the statistical study of measures of shape collected from a group of organisms. These measures can be taken directly from an organism under study (e.g., height, weight, skull length) or from an image like an x-ray or 3D computed tomographic (CT) scan. Because the focus of this project is the head, 3D CT images of the skulls of baboons and mice are being collected and measurements are being taken on these images. We use anatomical landmarks—points in space that correspond to the position of particular features on an object. The 3D coordinates of these landmarks can easily be used to calculate linear distances and angles providing a large dataset of measurements.
Figure 1. Example of skull landmarks shown as red dots on 3DCT image reconstructions of baboons (upper row) and mice (lower row). Landmarks are shown from the front (far left), the right side (second from left), the base or bottom of the skull (second from right), and from inside the skull looking from the top (far right).
Figure 2. Using landmark coordinate data, we can measure distances and angles between landmarks, such as the distance between landmarks R and S and the angle RST. These same distances can be calculated for each baboon and compared.
These measurements are then analyzed using morphometrics—a suite of methods that join biology with statistics. Morphometric methods enable the analysis of biological shape and change in shape in three dimensions. It has been shown that patterns of shape variation mimic patterns of genetic variation and reflect differences in development between organisms. By combining morphometric methods with genetic information, we can identify the genetic variation that corresponds to shape variation, which will ultimately help us understand the evolution of shape in the human head.