Baleen whales are unlike any other animal. They have evolved unparalleled specialisations for feeding, hearing, smell, cognition and - above all - the largest ever body size. These extreme features underlie the unmatched dominance of baleen whales in today's oceans. The origins of these key adaptations required major changes in the anatomy and function of the skull and teeth. However, exactly how and when the extreme innovations of baleen whales began remains an outstanding question in animal biology. This proposal aims to combine exceptional Australian fossils with recent advances in 3D imaging, biomechanics, and evolutionary analysis to discover how the secrets to the success of baleen whales first evolved.