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Species & Giraffe necks (was Re: tooth counts in systematics)



At 10:50 AM 4/12/99 -0400, Josh Smith wrote:
>L Nyveen wrote:
>> 
>> And all that leads right back to the old clumper/splitter debate.  You
>> can't decide what intraspecific/intrageneric variation is without first -
>> often quite subjectively - deciding just what makes a species/genus.
>> 
>       BINGO.  You see why spending all ones time deciding what sits 
>next to what on a cladogram is in my mind something best left to others.  
>We spent an entire semester seminar here just wrestling with the species 
>definition question and came to very very few satisfactory conclusions.

Seconded (not that I was in that seminar, but one similar enough).  Much as
I like the Specific Mate Recognition Species Concept in principal (at least
for sexually reproducing metazoans), there is just too much baggage and too
little testable with it to apply it effectively to most of the type of
material I work with.

The more time goes on, the more I agree with Horner on this idea: species
are unreal divisions of historical (natural) lineages.

Oh, and by the way, to muddy the waters of yet another basic tenant of
biology (in this case, homology), see Nick Soulunias' paper in the latest
_Journal of Zoology_ (I'll post the whole citation later today).  Lots of
nice stuff showing the decervicalization (or thoracization?) of the last
cervical of _Giraffa_, and the intercalation of a new cervical somewhere
between C2 and C6.  And all this AFTER the split between okapis and giraffes
(and, for that matter, between _Giraffa_ and a lot of the other big extinct
giraffids).

Yeah, so this can happen within a traditional mammalian subfamily, but
having the cuppage of _Opisthocoelicaudia_'s centra reverse modes is "too
improbable" for it to be a titanosaur.  Uh, yeah.  Right.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661