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Re: Phytodinosauria (re-sent)



[My apologies for any additional confusion: about the message that George
 sent and that I previously told you you didn't see...  George has
 resubmitted it.  Even though you should have already seen Jonathan's
 response to an earlier version of it, here it is. -- MR ]

In a message dated 96-09-27 12:56:44 EDT, znc14@ttacs1.ttu.edu
(Jonathan R. Wagner) writes (responding to my comments):
 
> >Laterally compressed, leaf-shaped teeth bearing marginal denticles to the
> >cutting edge; dentition heterodont with non-recessed, marginal cheek
> >teeth.
>
>         This describes Eoraptor.
 
Not at all. I have a photo of the skull in front of me, and even though the
photo is not of the best quality, the teeth look nothing like ornithischian
or prosauropod teeth. They're backwardly curved and serrated like ordinary
carnosaur teeth, and indeed remind me of the teeth of _Herrerasaurus_.
 
>        It seems that there was one really good way to make
> dinosaurian vegetarian teeth that kept coming up...  This is also
> why I think Sauropoda phylogenies which dependant on tooth shape are
> not good....  IMHO, the leaf-shape, or a predeliction to it, was
> genetically in the genome already, and was surpressed or expressed
> depending on the needs of the clade. ...This is one character, and
> not enough to build a clade upon.
 
Tooth shape can be quite distinctive within Archosauria and should not be
omitted from any cladistic studies (horrors). And--how could you possibly
tell whether the "leaf-shape" was "genetically in the genome already"
(whatever that means)?
 
>>To these I would add: ilium with well-developed presacral anterior process
>>embracing caudal dorsal vertebrae and/or ribs (uniting anchisaurid
>>Prosauropoda, Segnosauria, and Ornithischia)
>        Sounds like it's related to herbivorous habits to me...
 
Sauropods and "pre-anchisaurid" prosauropods do not have such ilia,
and they're herbivores, so how is this related to herbivory? There
will be figures illustrating the evolution of the phytodinosaur pelvis
from Sauropodomorpha through early Ornithischia in _Mesozoic
Meanderings_ #2.
 
>>Bakker gives one further character, the "double breast bone,"
>>or sternum comprising two unfused elements.
>        And he indicates that this is primitive for the dinosauria, if I am
>
>not mistaken.  Also, aren't there some theropods (Allosaurus?) which
>express this feature?
 
No, Bakker places this character at the node uniting sauropodomorphs and
ornithischians in his phyogenetic tree in _The Dinosaur Heresies_.
 
In the entire Cleveland-Lloyd Quarry not one bone has so far been identified
as a sternal of _Allosaurus_. Take a look at Madsen's _Allosaurus_ monograph
and see whether you can find one. We now know, however, that some of the
bones therein identified as _Allosaurus_ ribs are really furculae (see Dan
Chure's paper in the current JVP [which I haven't seen yet because of a slow
post office]).
 
> Indeed, if sauropodomorphs are placed at the base of "Saurischia"
> between Ornithischia and Theropoda, then (most parsimoniously) the
> common dinosaurian ancestor was herbivorous and theropods were
> secondarily carnivorous.

You misunderstand. I am arguing against placing saurpodomorphs at the
base of Saurischia by noting that it would make theropods secondarily
carnivorous unless herbivory evolved twice in neighboring clades
(Ornithischia and Sauropodomorpha), which is less parsimonious than
assuming it evolved once.
 
>I'm not saying that I think Phytodinosauria is necessarily
>polyphyletic...
 
Well, you can take a horse to water...