Dinogeorge Digest #2

[Dinogeorge@aol.com]

Subj:   Re: Birds (Re: WHAT I SAW TODAY AT NATIONAL GEOGRAPHIC)
Date:   98-06-26 01:24:40 EDT
From:   Dinogeorge
To:     znc14@TTACS.TTU.EDU

In a message dated 98-06-25 21:16:57 EDT, znc14@TTACS.TTU.EDU
writes:

<< George Olshevsky wrote:
 >I prefer defining birds (Aves: stem taxon) as all dinosaurs closer to
 >_Megalosaurus_ than to _Iguanodon_.
         Problem with this in phylogenetic taxonomy (which I don't believe
 you recognize, but anyway) would be that at least Cracraft and Gauthier have
 published different definitions than this, definitions with priority over
yours.>>

Priority is a free-for-all among taxa above the family level in zoological
nomenclature. Cope has priority over Marsh with Goniopoda over Theropoda, and
Marsh has priority with Coeluria over von Huene's Coelurosauria. Until the
method of defining taxa according to phylogenetic taxonomy is recognized for
all taxa by a suitably empowered authority, nobody has to accept phylogenetic
definitions for taxa. Zoological nomenclature is still Linnaean, like it or
not.

Now, this is not to say that I'm necessarily hostile to phylogenetic
definitions for taxa. Actually, I'm >for< it. It think it will, ultimately,
provide some stability in a pretty chaotic realm. The first thing that needs
to be done in dinosaur taxonomy, however, is to "clean house." That is, to
tabulate all the different higher-level taxa ever created for dinosaurs,
examine each one critically to see whether it can be fitted with a suitable
phylogenetic definition, and discard the useless and synonymous ones.

        << Also, aren't you succumbing to the same problem that exists with
the current definition of Dinosauria ("the most recent common ancestor of
 _Triceratops_ and birds and all of its descendants")? This definition is
 not, IMHO, a good one. As Dr. Holtz put it, this "makes birds dinosaurs by
 definition rather than by discovery.">>

Actually, I noticed this way back, and I even posted my opinion about this
(or a similiar definition published of Dinosauria). But this merely turns the
problem around. If we accept this definition of Dinosauria, then we know (1)
_Triceratops_ is a dinosaur, and (2) birds are dinosaurs. It remains to be
shown that such animals as _Iguanodon_, _Apatosaurus_, and _Tyrannosaurus_
are dinosaurs. Fortunately, I don't think this will be (or is) too difficult.
It would be interesting if Feduccia and Martin were (by some miracle) to
accept this definition of Dinosauria. They would then, surely, try to argue
that maniraptoran coelurians weren't dinosaurs but only came to resemble them
by convergence.

     <<    Especially given your rather novel theories about dinosaur
 phylogeny, I should think you would want the likes of _Megalosaurus_ or
 whomever be discovered to be a bird, rather than defined as such. Just a
 thought... >>

Yes, well, I think the evidence shows that _Megalosaurus_ was indeed a
bird--a theropodomorph bird rather than an avialan bird, of course.

Subj:   Re: secondary flightlessness (wordy)
Date:   98-06-26 01:24:25 EDT
From:   Dinogeorge
To:     jwoolf@erinet.com
CC:     th81@umail.umd.edu

In a message dated 98-06-25 20:39:05 EDT, jwoolf@erinet.com writes
responding to me):

<< > This is because I believe that avian flight
 > took tens or scores of millions of years to evolve, slowly and
 > incrementally-- allowing for the existence of thousands of potential
flying
 
 > ancestral species--
 
 Why? >>

For roughly the same reason that the Daimler Brothers didn't build a Pontiac
Trans-Am as their first automobile in the late 1800s. The first birds didn't
start out as powered ornithopters, and it took time for evolution to meander
along its random way. If it had happened overnight, we'd have a lot more
fossils of modern-looking birds in the Triassic and Jurassic than we do, I
think.

<<I think the ground-up theory is rather absurd too -- but I also think
it's quite likely that the small arboreal predator niche was colonized by
dinosaurs very quickly and very successfully, perhaps as far back as the
Triassic. 
These tree-dwelling coelurosaurs were probably something like the
"arbrosaurs" in Dougal Dixon's fanciful _The New Dinosaurs_.  Feathers then
evolved first as either insulation or camouflage, then as display mechanisms,
then became useful for gliding, and finally the arbrosaurs developed powered
flight.>>

I think you're quite right about Triassic diversification of small dinosaurs.
Even the earliest-known dinosaurs are already well separated taxonomically
into sauropodomorphs, theropods, and ornithschians. This implies that
considerable dinosaur evolution occurred prior to their appearance, sometime
in the Early (yes, Early) or Middle Triassic. The fact that such forms are
nonexistent in the fossil record so far suggests that they were all small
animals--something the size of lagosuchians, for example, or
_Longisquama_--and very rarely if ever preserved. Too bad. You can drive a
truck through this period of dinosaurian evolution.

Subj:   Re: secondary flightlessness (wordy)
Date:   98-06-26 01:24:13 EDT
From:   Dinogeorge
To:     jwoolf@erinet.com
CC:     th81@umail.umd.edu

In a message dated 98-06-25 20:39:05 EDT, jwoolf@erinet.com
writes:

<< It's an intriguing hypothesis, certainly -- but how does it explain the
 fact that the birdlike Cretaceous theropods are all recognizably less
derived than _Archaeopteryx_? >>

Same reason that extant ratite birds, such as ostriches, emus, and
cassowaries, are less derived than extant neognath birds: It takes time to
evolve from a small, arboreal form into a larger, cursorial form. But there
>are< flightless cursorial Cretaceous theropods more derived than
_Archaeopteryx_, such as _Patagopteryx_ and _Gargantuavis_. These are derived
enough, however, to be classified as birds by most workers. It would be nice
to have a flightless cursorial theropod that's just a bit more derived than
_Archaeopteryx_ but less derived than, say, _Iberomesornis_ or _Sinornis_,
but sometimes you can't have everything you want.