Sorry to disappoint, but no, the Jurassic mammal was not a mustelid.
Mustelids did not even exist until about 30 to 35 million years ago,
around 130 million years after this fossil unless there is new reputable
info on that since I last read on the topic.  The order Carnivora itself
didn't even exist until about 100 million years after this fossil, again
with the disclaimer (LOL!).
 
The animal to which you refer existed about 165 million years ago and
is the largest and most specialized mammal of that time found, about
the size of a very small (emphasize small) female ferret (around 18
ounces/500 grams), showing that mammals filled more niches than known for
the time and that at least one form of highly specialized mammals was
present so there likely were others, too, and is the first semiaquatic
mammal found so far by over 100 million years.  It also is the first to
be preserved with fur of two types -- dense undercoat and short guard
hairs.  This mammal also has features which indicate an ability to
burrow.  Vertebrae were like an otter's, and the teeth were fish eater's
teeth like seals have.  The name give is Castorocauda lutrasimilis which
literally translates to "beaver tailed" for the genus name, and "otter
similar-to" for the species name.  It was docodontan; a group which no
longer exists.
 
http://www.sciencemag.org/
and
http://www.sciencemag.org/cgi/content/abstract/311/5764/1123
and
http://palaeoblog.blogspot.com/
 
If docodontans sound familiar there was a recent study (last year, I
think) indicating that some may have been venomous.
 
Green feces indicates very rapid transit.  There are a range of possible
causes: some types of food borne bacteria (bloody flux is mentioned in
Fox's _Biology and Diseases_ in relation to salmonella which can be
gotten from food or from birds and reptiles, and I think maybe
amphibians, but that symptom is apparently not common.  See post like
http://ferrethealth.org/archive/browse.php?msg=SG6619,
http://ferrethealth.org/archive/browse.php?msg=SG12118,
and notice that
http://ferrethealth.org/archive/browse.php?msg=SG11178
among other things discusses treatment of gram negative bacteria.), some
types of parasites (coccidia, giardia which can be gotten by drinking
outside water or aquarium water, etc.), ECE (See
http://www.afip.org/ferrets/ECE/ECE.html and remember that secondary
complications like colitis can happen, but remember that there would
have to have been a disease exposure as with any other disease.) and
multiple other GI problems.  What tests have been done?  Has
Eosinophyllic Gastroenteritis been considered?
 
Influenza is a respiratory disease which can have GI symptoms, but always
has respiratory ones.  If there is no respiratory disease it is not
influenza.  There are certainly transient GI diseases, though.
 
Hydration is paramount in importance, and your vet is seeing to that.
Also, treating the symptoms.  If it is coccidia treat all vulnerable
individuals.
 
Anonymous, has the ferret's mouth and throat been checked by the treating
vet.  looking for things like sores or infection?  (If there are a number
of oral sores also check the kidneys.) Can the ferret swallow okay if
held vertically as happens with MegaE?  Have causes of dysphagia
(difficulty swallowing) been considered?  In dysphagia it is usually
harder to swallow thin fluids, so try making it into a soup and see if
that works.  Is this a neural crest variant ferret?  Dysphagia has not
been proven with these variants but both the nerves of the area and the
formation of the mandible can be altered by those genetic variants, so it
is hypothetically a factor.  Examples of the pelage of such ferrets are
life long ones with panda heads, head blazes, extraneous white spotting
that is not a cleanly margined and complete mitt and bib set.  If there
is dysphagia be extra careful to not force, because these individuals
are much more prone to inhaling the food or fluid so more vulnerable to
aspiration pneumonia.
 
-- Sukie (not a vet)
Ferret Health List co-moderator
http://www.smartgroups.com/groups/ferrethealth
FHL Archives fan
http://ferrethealth.org/archive/
replacing
http://fhl.sonic-weasel.org
International Ferret Congress advisor
http://www.ferretcongress.org
[Posted in FML issue 5169]