Jonathan, there is a large body of literature on this subject; the two
authors to go to first are Vera Eisenmann and Ann Forsten. For a handy
start on getting the references, look in the bibliography to Bruce
MacFadden's book "Fossil Horses."
Though they take somewhat different approaches, both Eisenmann and Forsten
are of the opinion that if you take enough measurements on enough
specimens, that you will then be able to tell equines apart
"statistically". I have never felt real comfortable with this, any more
than I feel that morphometrics per se can lead you to a grasp of the true
relationships within any group of animals. In short, I think that the
thing that most powerfully and accurately distinguishes one sort of animal
from another is shape, but shape cannot be ascertained by any set of
calipers, and cannot be specified by any manipulation, statistical,
algebraic, or otherwise, of the set of linearities that repeated caliper
measurements produce. In short: size cannot really proxy shape, no, not
even when you proxy it "to a limit of infinity".
Nonetheless, using size to proxy shape is the current professional norm,
and unless you bow to the god of the caliper and the T-test, you are more
likely to perish than be able to publish.
So I'm not asking you to take my advice -- only giving it out, like just
any other old fogey -- my advice might help you solve the problem, it
might foster your level of insight as to what equines are all about, but
it's not likely to help get you a job. I think that the only RELIABLE way
to tell equine species apart is to have complete, or nearly complete,
skulls. You can reference my "Stripes Do Not a Zebra Make" paper in
Systematic Zoology from 1982 to get the characters by which this
differentiation can be made.
Shy of having complete skulls, complete jaw rami and/or complete
associated rows of cheekteeth are pretty good. One can usually tell a
horse's jaw from a mule's or donkey's on sight. If you've got teeth, you
can look at the depth to which the ectoflexid penetrates, the separation
of the metaconid-metastylid loops, and the shape of the linguaflexid. In
the upper teeth you can look at the shape and relative length of the
protocone and the degree of wrinkling exhibited by the enamel, especially
that which rims the fossettes.
Shy of skulls, jaws, or teeth, you have cannon bones -- those of asses are
smaller and more slender, those of horses usually larger, but even if not
larger (or longer), then certainly broader and stouter, especially the
fore cannons. Mules will be intermediate. You can also pretty well make
the same assessment on proximal phalanges, i.e. horsemens' term "long
pastern bones", or indeed on any of the phalanges, again especially those
pertaining to the forefeet.
Next best after that would be just about any limb bone, the best perhaps
being the pelvis. If very small, it's almost certainly a donkey; if very
large, and especially if the ischium is relatively long, it's almost
certainly a horse.
Thoracic vertebrae esp. about T4-T8 of horses have longer dorsal spines
than those of donkeys, because domestic horses have been bred to have high
withers, whereas donkeys almost always retain the primitive condition,
which was pretty muttony.
Can't help you too much beyond this, except to say that it is very unwise
to stick your neck out farther than a tentative assignment or "c.f." for
anything shy of a complete or nearly complete skull. If you have a lot of
loose unassociated teeth, you may very well be better off with Eisenmann
and Forsten than me.
For the other old fogeys reading here, by the way, I had the amusing
experience this evening (at a wedding reception) of teaching a teenaged
boy how to use a manual typewriter (we were to type messages of
congratulations to the happy couple, who are also both silverhairs). This
young man now knows what a "ribbon reverse" and a "warped platen" are.
What will the world come to next. Cheers -- Deb Bennett
> Hello All,
>
> I am working on a faunal corpus containing equid bones. For the period
> under question there were known to be horses, donkeys, and mules at the
> site. How can these be distinguished (esp. mule and horse)? Any tips,
> references, or helpful advice will be greatly appreciated.
>
> Best,
> Jonathan
>
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