Q-N-A Teeth, Claws and Eyeballs
by Bob Church
Q: "Why are my ferret's teeth so long? Are they longer [in proportion] than in other species?" "It seems I am always cutting my ferret's nails. Do they grow extra fast?" "Why do ferret's have such tiny eyes?"
A: All the better to bite, render, and serve you up for supper, my dear. Nailed that one by the skin of my teeth, didn't eye?
All three are modified for the hunting activities of wild polecats--the ancestors of the domesticated ferret. The ferret just happened to inherit them. The teeth are long, but not proportionately longer than in many other species of the same size. Many civets, mongeese, and smaller wild cats also have "long" canines, and there is basically two reasons for this. First, small animals run a tremendous risk as predators; the prey species have a very real defensive ability and can (and do) kill them. The odds given in many of the older ferreting/ratting books place the ferret's odds at beating a Norway rat at about 50%. The long fangs possessed by the ferret are excellent for piercing the neck and skull bones, rendering an instantaneous death and saving the predator the risk of serious or mortal injury. The second reason is biomechanics; the larger the tooth, the "blunter" because the tooth needs to be thicker to withstand the biting and shearing forces placed on it during a kill. Skinny teeth snap off, as many a sad Smilodon can testify. But in smaller mammals, the teeth do not have the same heavy biomechanical forces and the teeth are thinner. This makes them look longer and sharper compared to a dog's tooth. Remember, wild polecats eat animals that are their body size or less, while animals such as wolves eat animals many times their body size.
Ferret nails are not much different from most other mammals, including ourselves. Technically, a nail is flat while a claw is curved, but some use "nail" interchangably. Ferrets have claws. At first glance, a claw (or unguicula) looks like it is a solid piece of kornified tissue, but it is actually a piece folded in the middle with the lower parts (the underside of the claw) near or touching each other, but not fused. So a nail is a flatened-out claw, see? Some species (and at least one reference suggests ferrets may belong to this group) have claws who's growth responds to use; that is, digging may help to make the claw grow faster (and usually stronger). In most species, the claw grows at a "set" rate. Claws in digging animals tend to grow at a faster rate than in most other mammals (save hoofed animals, perhaps), which is designed to offset their wearing down during digging. The shape, thickness and length of the claw reveals its use. A cat's claw is short, extremely curved and doesn't extend far past the interior bone (ungual process of the terminal phalange), a ferret's claw can extend quite some distance past the interior bone, while the badger has a claw that is almost a nail, and extends a great distance past the bony part. The main reason for this structural difference is due to the cat using it's claws for prey capture, compared to the ferret, which uses their claws for digging. Ferrets evolved as diggers, and the instinct can be hard to break, as many carpets can testify.
Ferret eyes are indeed proportionately smaller than in other animals of the same size. There are two basic reasons for this, the first being ferret have small eyes because they use their sense of smell as their primary hunting weapon. The brain cannot be larger than the skull which contains it, and since head size is allometricly tied to body size, there is not a lot of room for the brain to grow. But increasing the dependence on the sense of smell creates problems....where does all the increased wiring go? One nifty way to solve the problem of increased dependence on a single sense is for some other sense to decrease, allowing the more important sense to have expansion room in the limited space of the brain-case. Ferrets seem to have "opted" for this solution, decreasing vision and associated "wiring" to allow for the increase size of the olfactory expansion and wiring. Dogs "opted" for increasing both, which is why they have foreheads and the ferret doesn't--the forehead allowed expansion room for both thesense of small and vision. The ferret, or rather, the polecat, cannot afford a forehead to get in the way while running down tight burrows (Can't you imagine the sound, "trot, trot, trot, bump, ferret chattering fert-cuss words, trot, trot, trot, bump?") Second, because ferrets have such a strong adaptation to hunting in burrows, the smaller eyes help in keeping dirt out. Besides, burrows are dark, and eyes are not as important as with daytime killers.