An enduring focus in education on how scientists formulate experiments and "do science" in the laboratory has excluded a vital element of scientific practice: the creative and imaginative thinking that generates models and testable hypotheses. In this case study, final-year biomedical sciences university students were invited to create and justify a taxonomy of selected vertebrates on the basis of their brain organisation, as part of an exercise exploring the evolution of embryonic development. While raising a number of issues surrounding the context and methods of comparative zoology, this exercise also invoked a set of cognitive processes that can neither be adequately characterised as role-play nor critical thinking. By contrast, the act of formulating and justifying taxonomy identifies a style of creative thought that is a prerequisite for hypothesis formation. A defining characteristic of this exercise is that it engages activities that are independent of disciplinary perspective. This flexibility in approach may provide a route through to defining what qualifies as a creative teaching exercise in science. (Contains 1 figure.)