Dinosaur Taxonomy (was Re: Re: dinosaur flatware)

[pharrinj@PLU.edu]

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 
system.

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 
swift.

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.