"Ichthyostega probably used its paddle-like legs and tail to swim while in the water," she added. "The hind legs probably were not of much use on land, especially compared to the forelimbs."
Pierce and her colleagues Jennifer Clack and John Hutchinson reconstructed the first ever 3-D computer model of the tetrapod's skeleton. Ichthyostega, in addition to having big muscles, possessed huge fang-like teeth and probably ambushed its prey.
The model, which put together the fossils like a jigsaw puzzle in animation software, revealed that most books and museum displays showing Ichthyostega are incorrect. They usually represent this beast marching around like a large salamander with stocky legs.
Instead, the reconstruction determined that the shoulder and hip joint of this species prevented a conventional walking step, since its limbs were incapable of rotating along its long-axis. This motion is critical to locomotion for us and other modern land animals.
Earlier fish relatives of Ichthyostega and other tetrapods, called tetrapodomorphs, had the ability to rotate their fins. This allowed later animals to move well on land. The research was published in this week's issue of Nature.