The six-toed moldiwarp

The first 4-limbed animals evolved from fish in the swamps of the Devonian, some 350 million years ago. These early creatures had much the same bones in their limbs as we do but the numbers of digits on their limbs was rather variable; some species had 5, some 6 and some 7. Eventually, however, evolutionary forces seem to have favoured 5 fingers and 5 toes, a condition that has been conserved right up to the present day.
It comes as a bit of a surprise, then, to find that our subterranean friend the moldewarp, or mole, appears to have six digits on each paw! The photograph shows the right rear foot of a mole and it is clear that it has 6 toes, 5 with claws and 1 without. In fact the sixth toe isn't a normal toe but consists of just a single, sickle shaped bone that has been derived from a small bone in the ankle. The same is true of the hand, which has an extra clawless finger, again a single bone, this time derived from a small wrist bone.
The mole's extra digits seem to have evolved as adaptations to enhance its digging efficiency. The mole digs with its spade-like hands and the extra fingers increase their surface area. The feet are used to brace the mole against the tunnel wall whilst digging and the extra toes help it grip tightly.
Evolution is indeed a thing of beauty and wonderment!