<p>This article examines the distribution of cognitive capacities across animal taxa and advances an organizational account of the evolution of conscious agency. It explores how vertebrate and invertebrate body plans have shaped brain evolution and embodiment. The central thesis is that while invertebrate body plans generally constrain brain development, the vertebrate body plan has facilitated brain complexification and bodily integration. A key focus is the exceptional case of coleoid cephalopods,the only invertebrates to evolve large brains. Despite their remarkable cognitive abilities, these animals remain a borderline case of conscious invertebrates. Although they probably exhibit a form of consciousness, their body plan limits both brain complexification and evolutionary diversification, preventing them from following the same trajectory as vertebrates. We examine the reasons why only the vertebrate body plan has enabled the sustained expansion of cognition, leading to greater complexity and diversification. Finally, the paper argues that the evolution of conscious agency in vertebrates results from a distinctive form of embodiment: a feedback loop in which bodily development supports brain growth, which in turn enhances bodily integration, fostering further brain complexity in a self-reinforcing process. The article concludes with reflections on the significance of conscious agency as a major evolutionary transition in animals.</p>