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Birds, Fish, and the Class Ceratopsia (was RE: Response to Gould?)



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Zoe Heraklides
>
> >Ho-kaaaaaay...here we go again with the "elephants are fish" argument!
> >Elephants are NOT fish and Birds are NOT Dinosaurs. I will now run for
> >cover.
>
> Yes, birds ARE dinosaurs, just as they are archosaurs, diapsids and
> amniotes.  That is a phylogenetic reality (at least based on abundant
> evidence).  Elephants are therapsids, just as they are synapsids and
> amniotes.  It is whether "birds" should be called dinosaurs which is the
> casus bellus here.  I don't think paleontologists are advocating that
> people, in everyday vernacular usage, should abandon the noun "bird" in
> favor of "dinosaur".  That's silly.  To claim that this is what
> paleontologists are advocating is a misrepresentation of their
> views, with a
> pinch of mischief added to the mix.
>
> Nevertheless, birds do seem to be descended from dinosaurs, and as such,
> must be regarded as dinosaurs.  Elephants did descend from some type of
> fish.  The "fishes" represent several clades of (primitively)aquatic
> vertebrates; in a sense, the fishes are the non-tetrapod
> vertebrates.  The
> term "fish" is phylogenetically meaningless; the term
> "vertebrate" is more
> appropriate in this context.  Elephants are vertebrates?  I can live with
> that!  ;-)
>

Zoe,

Well said!  I've been busy, and would have responded sooner, but you have
made several of the same points I was going to (i.e., that "fish" is not
used in any real phylogenetic sense, while "bird" is; that most people would
be comfortable calling a dog or elephant or bird a vertebrate).  Also, as
you (and Norm King, to a degree) point out: context is important.

Which is why I will add some more: context IS important, and this is why we
*should* refer to  birds as living dinosaurs (okay, except for those who
reject the dinosaurian origin of birds).  Why? Because to not recognize this
is to lead to falsehoods and imprecise thinking.

Examples:
1) Were dinosaurs warm-blooded or cold-blooded?  Well, we know that living
dinos ARE warm-blooded.  The question is properly "when in the evolution of
dinosaurs did warm-bloodedness evolve?"

2) Dinosaur extinction.  The dinosaurs did NOT all become extinct at the K-T
boundary, any more than the cephalopods or foraminiferans or marsupials did.
All these groups took major hits then, but managed to survive.  By
refocusing our attention to examining why neornithines survived while all
other dinosaurs snuffed it opens research frontiers which are closed by
grade-based thinking (e.g., "Well, all dinosaurs died out with the K-T
impact.  Case closed.")

3) Dinosaur appearance & behavior.  (Already addressed in this thread, so I
won't say more).

Ken Kinman added a take that birds should not be called dinosaurs because
they are "sufficiently different".  To this I reply: how?  What anatomical
features or morphological gap separates birds and their kin?  Most of the
classics (feathers, furculae, pygostyle, toothless beaks, etc.) are either
more widely distributed among theropods than previously known or are not
present in _Archaeopteryx_ and other basal forms classically considered
"birds."  (In fact, a few more features that currently are used to diagnose
the _Archaeopteryx_ + later bird clade are about to fall by the wayside:
stay tuned!).

There are *no* big morphological jumps between the derived maniraptorans to
the exclusion of birds on the one side and _Archaeopteryx" and later birds
on the other.  This should come as no surprise: evolution happens.  Big
morphological breaks say more about a poor fossil record than the
distinctiveness of the derived taxon.  In group after group after group, the
discovery of forms deeper and deeper on the tree greatly reduce the
morphological "distance" between groups.

On the other hand, I can see an appeal to using morphological
distinctiveness as a means of classificiation.  However, I wish that users
of a rank system would truly stick to their guns and REALLY use
morphological distinctiveness.  For example, Class Aves (excluding
dromaeosaurs and troodontids and other classic theropods) was at one time
separated by a morphological gap (in our knowledge of small theropods and
their integument!), but now there is no anatomical structure found in
_Archaeopteryx_ which is not also found in some other small theropods.  In
contrast, Ceratopsia is characterized by a rostral bone.  This is a
neomorph, folks: it is a whole new bone that no other animal has!  If whole
new anatomical elements aren't grounds for very high level classification,
than what is?

So, I would like to see gradists support me (;-) in elevating Ceratopsia to
Class rank. If they truly accept morphological distance as a guiding
principle, let's seem them do it.  If in fact they are simply maintaining an
old tradition for its own sake, regardless of the supposed guiding
principle, then they will keep Ceratopsia an Infraorder.

                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