The question is, can the morphology of the back of the skull indicate the
degree of "fitch?" At last! A question quite similar to one asked in my
orals, and a major portion of my PhD!
 
First, bone is a very plastic medium, one that is constantly being replaced
in living creatures.  In addition, it changes according to the load put on
it through the use of muscles.  The bone of a computer jockey would be
readily distinguishable from a weightlifter.  Bone responds to stress,
growing and thickening to strengthen the bone from within to protect it from
injury from without.  The ads say milk builds strong bones, but the truth is
exercise does.  So how does this relate to ferrets?
 
Mastication, cage confinement, and burrowing.  (Yes, I masticate serval
times a day, and am damn proud of it, buster!) The muscles that are used for
these three activites directly influence the size, thickness and shape of
the skull.  In mastication, diet alone can cause changes in skull
morphology.  For example, the force required to cut kibbled pellets (we are
refering to meat-eating carnivores-like the ferret-possessing a carnassial
tooth) is different than for swallowing wet canned food, which is different
from eating the body of a vole or rabbit.  It takes very little force to eat
the chopped and cooked wet food, "normal" force to eat the carcass, and
greater force to cut up dry kibbled pellets.  The muscle scars and insertion
points will be different for each diet (assuming a long-term consistancy).
Large females might be misidentified as small males, or species differences
might be overlooked or mistaken.
 
Animals kept in cages have far less muscle tone than those making a living
in the wild.  If you are impressed with the skills of the ferret, you should
see a polecat.  Its like comparing a ranch mink to a wild one.  Confinement
effects morphology, pure and simple.  Most of the muscles that work the neck
also attach to the skull, and are quite important in burrowing.  So there
would be differences in comparison bewteen the a confined animal and a feral
one, which is the major argument I have heard, and made, to distinquish one
population from the other.
 
I wish it were that easy.  What about the confined pet eating dry kibble?
What about the fitch living in barns or rocky regions, and not actually
doing much tunneling?  The only time you can trust a scientific answer is
when all possiblities have been investigated for a single question.
Nonscientists have no idea how difficult that is.  The best answers of
respected icons of science have been thrown out by the singular dumb grad
student who says, "Well, what about (place your favorite unrealized
possiblity here)?  Could that be a factor?"
 
The way it works is, genetics gives you the possibility of a specific
product, such as the shape of the skull.  Like a skewed potter's wheel, the
environment/environmental factors effect the change of the possibility into
reality, and the end result is often quite different than originally
intended.  In order to make predictions, such as "These skulls belonged to
confined ferrets, and these belonged to feral fitch, and these belonged to
wild polecats," you have to be able to identify all possible processes which
change the shape of the skull, and account for them.  I know of several
people working on such things, myself included, but know of no one who has
solved the puzzle.
 
The bottom line is, it's hard enough to distinguish ferrets from polecats;
distinquishing a feral state from the captive state is extremely difficult,
and yet to be proved with large populations.  (I've seen similar things with
small numbers of individuals; but increase the population, and the
differences disolve.).
 
In addressing the hybrid issue, good luck.  The degree of variation in
polecats alone overlaps the degree of variation in the ferret portion of the
population so much that any hybrids would be lost in the shuffle.  Draw two
overlapping circles.  One circle represents ferrets, and the other
represents polecats.  The region of overlap represents ferrets that look
like polecats, and polecats that look like ferrets.  That is the region
where you will find the hybrids.  So which is which?  You are a better
osteologist than anyone I know if you can distinguish them.  You could never
accurately know if the skull was a polecat, a feret, or a hybrid.  Sure, you
can breed a ferret with a polecat to get a hybrid, then compare the skulls
and find differences, but you already know what you have, and that
influences the results.  Try it with a large unknown population, and the
results will be humbling.  Extremes are always easy to tell--but "ferreting"
out truth with data overlap is next to impossible.
 
There was one study that claimed 100% reliablity in telling wild from
captive animals, but it used the teeth, not the skull per se.  The skulls
were separated into age classes based on the degree of fusion of bones in
the skull.  Within age groups worn teeth came from ferets/polecats fed dry
kibbled pellets, and teeth with lots of tartar came from beasties fed wet
foods.  Ferrets/polecats fed animal carcasses had low tartar buildup, and
low tooth wear rates.  This finding has not been retested to see if it holds
true.
 
Now, bust the bone into small pieces, disolve parts aways with acids, and
throw some away, and then try to tell the difference between the three
groups. That is what will have to be done to find the true ancestor of
the ferret. Any volunteers?
 
Bob and the 13 Showmes
[Posted in FML issue 1527]