had eight digits, while the more derived Ichthyostega had seven digits, the yet-more derived Tulerpeton had six toes.

Tetrapods evolved from animals with fins such as found in lobe-finned fishes. From this condition a new pattern of limb formation evolved, where the development axis of the limb rotated to sprout secondary axes along the lower margin, giving rise to a variable number of very stout skeletal supports for a