One of the great mysteries regarding the evolution of animals is how and when tetrapods (four-limbed vertebrates) achieved the ability to stand and move on solid ground. Old perceptions that our fish ancestors gradually evolved limbs with digits on terra firma have been discarded in light of new evidence favoring a wholly aquatic origin. This scenario implies tetrapods transitioned from swimming in water to walking on land at some point during their evolutionary history. But, which pioneering tetrapod species could move on land and how well? Did tetrapods walk out of their watery habitat on all four legs or were there intermediate locomotor ‘steps’ along the way? Using 3D modeling techniques and ancient muscle reconstructions, I will demonstrate that the earliest tetrapods (based on body fossils, e.g., Ichthyostega) may have lacked the limb mobility and musculature critical for walking. Instead, it is hypothesized that the front and back legs performed divergent functions: on land, the front legs may have been used simultaneously to pull the animal over muddy substrate; while in water, the back legs may have acted as flippers for swimming.