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RE: Ligers and tigrons - oh my!



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> zone65
>
> What makes lions and tigers distinct species, instead of just
> different breeds of big cat? Is this where cladistics comes in?
>
> Peter Markmann

As I mentioned in some emails recently, the ability to interbreed with
relatives is a primitive trait.  Thus, the cornerstone of the BSC
(Biological Species Concept) is based on plesiomorphy (i.e., the lack of
evolutionary change)!!

So don't let the fact that all of us learn the BSC as the "real" species
definition get in the way of the fact that it doesn't really work.

Species boundaries, like pornography, are hard to define.  Most of us can
agree on some of them: lions and tigers, for example, differ dramatically in
terms of behavior, external appearance, etc.; as do polar bears and
grizzlies.  Other times, however, they get harder to recognize if they are
distinct.

Similarly, genetic distance-based species concepts are even weaker than
macroscopic (behavior + morphology + range + whatever) species concepts: at
present, no one has really demonstrated that there is a distinct genetic
distanct which corresponds to universally-accepted morpho/behaviorospecies.
Genetic distance WITHIN different universally-accepted species can be
extremely great: a single population of chimps in Gombe can show as much or
more genetic distance between its members as there is in all of humanity!

So I would take genetic-distance based species with a grain of salt, which I
would then throw out or use on fries or something, because that's a better
use of salt...

In brief (too late), study of what actually goes on in Nature throws
conventional classroom wisdom on its head.  Species, or at least species
boundaries, are largely artificial human constructs, while higher taxa
(clades) are reality.

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Allan Edels
>
> Peter, et al:
>
> Aside from the obvious differences in coloration and environmental
> preferences, there is at least one difference noticeable in the skulls:
> If you take the skulls (minus lower jaws) of a lion and a tiger and
> place them on a table, one of the skulls will easily rock back and forth
> and the other will not.  (I'm not sure which is which - I think the lion
> skull rocks easier).  Thom H. can correct me on this.  [This difference
> is in the dentition of the animals, and the shape of the upper jaw -
> sorry, no real scientific nomenclature here].
>
> Note that I recommend that both animals are dead before you try this
> experiment :-).

The lion rocks, the tiger stays in place.  Hence, Smilodon really is a
sabre-toothed "tiger"... :-)

Both the experiment and the Smilodon comment were passed on to me from John
Ostrom, who learned it from one of his grad advisors.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796