Birds & dinosaurs have no class (long)

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>From Phillip Bigelow
>  So, why does the archaic (yes, archaic) Class AVES
>still continue to be used in systematics?  It certainly isn't the
>state of science that is maintaining this psuedo-class!

Aves (either Archaeopteryx & all later birds [traditional usage] or the
most recent common ancestor of all modern birds and all of that ancestor's
descendants [phylogenetic taxonomy]) is one of the best defined of all
vertebrate groups.    Nothing (short of proving avian polyphyly) will cause
the abandonment of this name.

> I can't believe that resistence from such people as Larry Martin
>is holding up the final abandonment of the Class AVES.

He isn't.  Aves is universally accepted among systematicists, although used
for two different clades (those mentioned above).

>  Birds are in the Class DINOSAURIA, not AVES.  AVES is dead.  Someone
>get a shovel and let's all go out and bury it.

Don't bury Aves.  Don't bury Dinosauria.  Bury the "Class" concept (more on
this below).

>John Ostrom, strangely, believes that AVES should be
>retained.  I can't figure out why he, of all people, would want this.

John follows a fairly traditional, gradistic taxonomy.  He agrees that
cladistics is a useful technique for determining relationships between
groups, but isn't so hot on a purely cladistic taxonomy (in which the only
valid names are monophyletic groups).  The same can be said of many
paleontologists, including several posters on this net).

>From Ken Carpenter
>True, from the dinosaurs' point of view the characters uniting it to the
>birds are synapomorphies, but from the birds point of view, those
>characters are symplesiomorphic (shared primitive characters).  Why not
>recognize all the autapomorphies that birds share, thus keeping Aves?
>(Yeah, I know I'll catch flack over this one, so what else is new?)

You won't catch flack from me, or any other cladist I know of.  Birds are
united by many characters not shared with any other organism.

>From Michael Chartier
>        If you're a strict cladist (which I am not), you will want
>to include birds with theropod dinosaurs, just like you will want to
>include humans and pongids (chimp and gorilla) into a single taxon,
>namely hominids. But to do this is to take away what is "special"
>about the group concerned. It is clearly evident that humans are much
>more derived than either chimps or gorillas are, so why not recognize
>their unicity (is that a proper word?) and retain them in hominids, to
>the exclusion of chimps and gorillas?

[Actually, the type of Pongidae is Pongo pygmaeus, the orang-utan.  Almost
all primatologists and paleoanthropologists agree that the African
anthropoids (gorillas, chimps and bonobos, and hominids) all share a more
recent common ancestor with each other than with orang-utans and their
extinct relatives.  A typical taxonomy for the "higher apes" nowadays would
have Pongidae (including Pongo, Ramapithecus, etc.) and Hominoidea, an
unresolved branching between Gorilla, Pan, and Hominidae
(=Australopithecus, Paranthropus, Homo).

And, trivia of the day, chimps were originally placed in Homo as Homo
troglydytes Linneaus (now Pan troglydytes).]

Phillip Bigelow, again:
>Putting dinosaurs into their own Class seems to be a less inflamatory issue
>than is moving birds out of Class Aves.  One reason for this could be the
>rigidity of classical Linnaean systematics. One question that needs
>to be asked is whether the Linnaean system was constructed
>with the provision that it could be ammended?  It appears, to me, at least,
>that Linnaean systematics is not easily ammendable, at least compared to
>cladistics.

Bingo.  A growing number of researchers (myself included) have recognized
that a fixed number of Linnean "ranks" (Order, Class, Division, Cohort,
etc.), even with a dozen or so preficies (super-, sub-, infra-, min-, mir-,
hypo-,  etc.) is still insufficient to reflect the number of bifurcations
in the cladogram of Life.  Furthermore, workers begin to get hung up on the
"meaning" of a particular rank (such as this discussion, is Aves a Class?
or is Dinosauria a Class?).

The most common solution currently is drop any pretense of Linnean ranks,
and recognize clades (an ancestor and all of its descendants) instead.  The
search is for nested relationships, not some Aristotelian Ideal of "Class"
or "Infraorder" or what have you.  In the current case, Aves represents a
diverse clade within the more inclusive clade Dinosauria.  Aves is
certainly a very derived bunch of dinosaurians, but they stem from a
dinosaurian ancestor.

An alterantive is the parataxonomy of George Olshvesky.  I haven't seen
others follow the particulars of this system yet, but I do know of several
paleontologists who follow its ideals.  Basically, parataxonomy explicitly
recognizes paraphyletic groups - those with a common ancestor but not all
of its descendants.  Paraphyletic groups have Linnean rankings, but are
prefaced by the word "para-" (Parafamily, Parasuperorder, Parainfraclass,
etc.).  In Olshevsky's system, Dinosauria is a paraphyletic group within
the Parainfraclass Archosauria, and neither Dinosauria nor Archosauria
contain Aves.

I have philosophical objections to parataxonomy, but (from various comments
posted on the net and elsewhere), I suspect others don't.

So, in my opinion, Dinosauria is a useful concept, Aves is a useful
concept, but "Class" is not.  Keep the first two, abandon the last.

Hope this helps,

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.