Selection for cognitive ability has been proposed as a key factor driving the evolution of larger brains and/or the brain structures associated with problem solving, social behavior and other cognitively demanding tasks. Major brain structures are often subject to different selection pressures, resulting in a significant degree of variation in brain size and complexity across vertebrates. Although cartilaginous fishes were previously thought to have relatively small brains with a limited behavioral repertoire, these fishes have brain/body ratios that are actually comparable to birds and mammals. This talk will explore major evolutionary patterns of brain organization in cartilaginous fishes, and how the relative development of major brain structures reflect an animal’s ecology, even in phylogenetically unrelated species that share certain lifestyle characteristics. I will elaborate on the novel techniques we are employing, such as magnetic resonance imaging (MRI), 3D printing, and flow cytometry, to push the boundaries of evolutionary neuroscience and digital dissection, allowing for both traditional and non-invasive exploration of evolutionary questions. As a perfect ‘bioindicator,’ variation in brain development can allow us to make predictions about sensory and behavioral specialization across species, highlight transitions in life-history stages within a single species, and predict the fitness consequences of anthropogenic disturbances and environmental change. These data pave the way for predicting cognitive function and/or more complex behavioral repertoires in fishes, with implications for how “intelligence” has evolved across vertebrates.