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Dinosaur Taxonomy (was Re: Re: dinosaur flatware)
On Wed, 10 Jan 1996 Dinogeorge@aol.com wrote:
> In a message dated 96-01-10 22:13:05 EST, pharrinj@PLU.edu writes:
> >I don't think there is ANYONE out there, though, who will agree
> >completely with this arrangement, though. (Thomas Holtz and Dinogeorge:
> >note that I've gone and changed it again!)
> I could go along with your classification of Phytodinosauria...
And, just out of curiosity, what's wrong with my Sarcodinosauria
(Herrerasaurs + Theropods)? It only took one good look at
_Herrerasaurus_'s hand to convince me that it is most probably a member
of the sister taxon to the Theropoda. I do not consider it to BE a
theropod, because I like Greg Paul's criterion that metatarsal I in true
theropods does not reach the ankle.
BTW, I still consider _Eoraptor_ to be an outgroup to all other
eudinosaurs, even after reading the description. The skull in
particular (somewhere between _Coelophysis_ and _Plateosaurus_, with both
leaf-teeth and blade-teeth) seems appropriate to an animal near the common
ancestor of sarcos and phytos.
All in all, I think my revisions make quite a reasonable classification
I do not think BCF and BADD are entirely mutually incompatible. They
seem to me simply to be different hypotheses about the form of the
animals on the stem of the cladogram (if you catch my meaning), and I
think both are probably applicable at various times. I do not think that
the last common ancestor of _Rioarribasaurus_ and _Lesothosaurus_, say,
could fly; but I think it is quite reasonable to think that many theropod
groups arose from small, maybe arboreal, ancestors.
In fact, here are a couple of scenarios that you might appreciate:
The arctometatarsalian condition (sensu Holtz) has often been interpreted
as an adaptation for running. I, however, have trouble seeing what sort
of advantage such a configuration would confer on a running animal.
_Noasaurus_, _Oviraptor_, _Allosaurus_, and _Compsognathus_, for
example, do not have arctometatarsi, yet they appear to have been quite
I propose that arctometatarsaly may have arisen as an adaptation for
perching. The earliest discernible arctometatarsalian *appears* to have
been _Archaeopteryx_, which I am willing to admit was probably arboreal.
One advantage conferred by arctometatarsaly is closer apposition of the
toes, thereby improving the foot's grasping ability (at least, that
appears to be the case in modern birds). This is of no use to a running
animal but would be quite useful for a perching animal. Perhaps it was
just by chance that the same condition was later passed down to large,
cursorial forms like _Troodon_, _Ornithomimus_, and _Tyrannosaurus_.
Another possibility (highly conjectural) is that the hyperextensible
second toe seen in _Archaeopteryx_ and dromaeosaurs might have started
out as an adaptation for climbing around in trees. Perhaps by bringing the
second toe up past the level of the other toes and digging the claw into the
bark like a logger's spike, the dino-bird ancestor of _Archae._ and
dromaeosaurs could get a better grip on trunks and branches. This would
later prove to be a good exaptation for a weapon, as in dromaeosaurs.
Just a thought, and possibly a half-baked one at that.