Magnetic Resonance Imaging (MRI) is a noninvasive way to acquire high-resolution images of soft tissue structures. We are using this technology to obtain high-resolution brain images from a range of cartilaginous fishes (or chondrichthyans: sharks, skates, rays, and chimaeras), who occupy a variety of habitats and are phylogenetically diverse. Despite the importance of their basal place in vertebrate evolution, little more than qualitative data has been available on variations in chondrichthyan brain organization and the implications these variations have for evolutionary adaptations has not been quantitatively unexplored. Using specialized software, the five major brain structures (telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) can be digitally segmented from MR slices and reconstructed into 3D images, providing new data on structure volume, surface area, and surface curvature, which can then be compared between species to help elucidate the evolutionary selective pressures that shape the brain.
- Yopak KE, Frank LR. Brain size and brain organization of the whale shark, Rhincodon typus, using magnetic resonance imaging. Brain Behav Evol, 74: 121-142, 2009.