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Paleospecies and modern species (was RE: LIONS & TIGERS REVISITED)



> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> darren.naish@port.ac.uk
> Sent: Tuesday, September 26, 2000 7:15 AM
> To: dinosaur@usc.edu
> Subject: LIONS & TIGERS REVISITED
>
>
> George wrote...
>
> > E.g., lions and tigers are skeletally indistinguishable (any
> putative
> > differences are swamped by individual variation within each species)
>
> Sorry, this is untrue - thanks to recently published reviews (see Turner
> and Anton) their skulls can be reliably distinguished: in the postcrania
> tigers are generally more robust. Incidentally, most cat workers do not
> think that lions and tigers are particularly closely related:
> lions are part
> of a 'spotted clade' that includes jaguars and leopards - tigers are
> outside of this group.
>
Indeed.

And yet, lions and tigers do produce offspring that are themselves fertile
(at least in crosses back to tigers: don't know if ligers or tigons can
produce offspring with lions).

This just goes to show something we've talked about here before:
Species criteria and species definitions are blurry in the modern world.
There is no good all purpose algorithm for identifying living species, much
less extinct ones.

Yes, there are sibling species in the modern world: taxa morphologically
identical but which do not interbreed due to differences in timing of
fertility, specific mate recognition sounds, etc.  And there are also
populations with a lot of ecophenotypic variation (_H. sapiens_, _Syncerus
caffer_, etc.) which show a lot of morphological regional or even
intraregional variation, which nonetheless are good "species" under most
senses of the term.  In fact, in _Syncerus caffer_ (the Cape buffalo) there
type of variation in horn size, horn shape, whether the bosses meet in the
midline or not, are the sorts of things that paleontologists would probably
use to recognize distinct species (or in the case of splitters, distinct
genera).

There is no single good answer as to how to recognize a species.  Thus there
will *always* be  conflict between different works on the hypodigm (specimen
composition) of a particular fossil or modern species.  This is something we
will just have to accept, barring the discovery of a really effective
species recognition algorithm.

As such, both the splitting and lumping extremes will have to recognize that
*neither* side is "right"; they simply have two alternative methods of
dividing up the specimens.  There are good arguments for both sides, but at
present it is difficult to frame these statements in a testable, falsifiable
framework.

                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