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Re: Differences between *Vancleavea* and thalattosaurs



Jaime, Sorry you missed the "see above" comment, (re: various fenestra, short 
snout, etc. plus the ref to Miodentosaurus, Askeptosaurus). 

Okay, my cards are on the table. Characters below shared with Askeptosaurus OR 
Miodentosaurus or both (quite a variety between them!) and not shared with 
proterochampsids AND erythrosuchids (the bounding taxa for Vancleavea, sensu 
Nesbitt et al.)

1. Skull shorter than cervical series
2. Nasals separated by premaxilla ascending process (that's the "neomorph" in 
Vancleavea and the related: Premaxilla contacts frontals
3. Frontals longer than nasals
4. Antorbital fenestra absent
5. Upper temporal fenestra closed or slit-like and the related: 
Postorbital-parietal contact long (extensive)
6. Parietal skull table broad
7. Surangular shelf (ridge) absent
8. Mandibular fenestra absent
9. Cervicals decrease in size anteriorly
10. Metacarpal II is the longest metacarpal
11. M4.3+m4.4 fused
12. Fourth trochanter absent
13. Metatarsals II-IV not shorter than half the tibia
14. Metatarsals I and V are wider than II, III and IV
15. Pedal digit IV not narrower than III

Granted, other than these characters, between Erythrosuchids and 
Proterochampsids, one or the other includes one character or another of 
Vancleavea, which in itself is amazing, but are we sure we don't know any 
intervening taxa between the erythros and proterochampsids? They share very few 
synapomorphies suggesting that nesting may be by default in the Nesbitt study.  

Finally, I reduced my taxon list to match Nesbitt, et al. 2009. + Askeptosaurus

Doing nothing else the tree resulted in 499 steps. Mesosuchus was the outgoup. 
In ascending order I found (Askeptosaurus +Vancleavea), Prolacerta, 
(Chanaresuchus + Tropidosuchus) Proterosuchus, Erythrosuchus, Postosuchus, 
Sphenosuchus (substituting for Dromicosuchus which was not in my database), 
Herrerasaurus, Coelophysis.

moving the Proterochampsids to the Nesbitt order results in 510 MPTs
moving Sphenosuchus to the Nesbitt order results in 518 MPTs
moving Vancleavea to the Nesbitt order results in 566 MPTs
removing Askeptosaurus from inclusion so the set matched the Nesbitt set 
results in 505 MPTs

moving Vancleavea to the outgroup or just inside Mesosuchus, where it nested 
originally resulted in 492 trees and moving Vancleavea between Proterosuchus 
and Erythrosuchus resulted in 501 trees.

I would be the first to agree with regard to scoring that when one considers 
other possibilities, one sees other possibilities. An example would be the 
neomorph bone of Nesbitt et al. which they could not identify because none of 
their sister taxa have an extended premaxillary ascending process. All of my 
sister taxa do, so identification was easy. 

Second opinions may not always be right, but in some cases they do shed light 
on alternate possibilities. I would love for Vancleavea to be a little armored 
erythrosuchid. It LOOKS like one. When I first saw it several years ago, that's 
all I could think that it was. When I looked at my PAUP results, that's the 
first place I looked. It wasn't there. When I found it in the thalattosaurs I 
took a deep breath and realized, well, that explains a lot-- but it also raises 
several questions.

Heck, that's why we all love this sport!

So, your turn. Have at it.

DP


On Dec 6, 2009, at 7:34 PM, Jaime Headden wrote:

> 
> Shortly after losing the ability to access my email, I gain it again. Good 
> boy!
> 
> Onto the show:
> 
> Dave Peters wrote (adressing me):
> 
> <I get the impression that you are "defending the status quo" by noting
> that you chose to report on only those few minor characters that would
> tend TO support the Nesbitt et al. results, rather than say, "attaboy,
> Dave!" and report on all the major traits (see above) that tend to NOT
> support the Nesbitt et al. results.>
> 
>   After examining your original post that started this, and the ones that 
> followed, I note that you have made no original contribution to asserting 
> which features link *Vancleavea* to any thalattosaur. Each feature noted was 
> brought up by someone else to which you've replied (and have been replied to 
> in kind). If you do wish to bring up original distributions, I suggest 
> actually doing so instead of waiting for someone else to try to set up their 
> own dummy to knock down an hypothesis you suggested but have not actually 
> formulated. That is, actually bring up features that link *V. campi* to any 
> thalattosaur to the exclusion of an archosauromorph and the analyses of 
> either Parker and Barton (2009) or Nesbitt et al. (2009). It is this lack of 
> content from you, Dave, that means that until you do, there is no other work 
> OTHER than those works which produce any sort of "status quo."
> 
> Cheers,
> 
> Jaime A. Headden
> 
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> 
> 
> "Human beings, who are almost unique in having the ability to learn
> from the experience of others, are also remarkable for their apparent
> disinclination to do so." --- Douglas Adams (Last Chance to See)
> 
> 
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
> Backs)
>                                         
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