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Re: Vancleavea campi - what is it? - not an archosauriform.



As descendants of the sister to Petrolacosaurus, thalattosaurians are 
definitely diapsids with a reversed temporal condition, same as Araeoscelida 
and mesosaurs and a bunch of others with absent lower temporal bars.  

The antorbital fenestra goes with Dakosaurus, not above named taxa, but you 
apologized earlier for that. 

If you're not sure what I mean about thalattosaurians, check out the previously 
listed refs. It's all there ready to test.

David Peters


On Dec 5, 2009, at 4:00 AM, Jaime Headden wrote:

> 
>   David, I am not sure what you mean about thalattosaurians, but 
> thalattosaurus (from *Askeptosaurus* to *Dakosaurus*) possess both 
> supratemporal fenestrae as well as antorbital fossa and fenestrae. The former 
> feature makes thalattosaurs (if non paraphyletic) firmly ensconced with the 
> diapsid condition, and therefore members of Diapsida. If, as previously 
> argued, you think the diapsid condition cannot reverse to the anapsid 
> condition, this should be pretty firm evidence for placement of thalattosaurs 
> (again, if nonparaphyletic) within Diapsida (but don't take my word for it, 
> read the Rieppel works instead). The latter feature is a common argument for 
> archosauriform phylogeny, and does not seem to occur outside of it (based on 
> the common occurance of crania with the fenestra to be found instead the 
> structure assumed to be Archosauriformes by its definition).
> 
> Cheers,
> 
> Jaime A. Headden
> 
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> 
> 
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> 
> 
> "Ever since man first left his cave and met a stranger with a
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> 
> 
> 
> 
> 
> ----------------------------------------
>> Date: Fri, 4 Dec 2009 21:59:07 -0600
>> From: davidpeters@att.net
>> To: dinosaur@usc.edu
>> Subject: Vancleavea campi - what is it? - not an archosauriform.
>> 
>> One of the reasons why Vancleavea campi does not have an antorbital fenestra 
>> and upper temporal fenestrae is because it is not an archosauriform. It is a 
>> askeptosaurid thalattosaur and a sister taxon to the short-snouted 
>> Miodentosaurus. [Links below]
>> 
>> http://2007tga.cgu.org.tw/cdrom/Oral%20(PDF)/ST1-4B-06.pdf
>> http://www.ivpp.ac.cn/cbw/gjzdwxb/xbwzxz/200902/W020090813372748918302.pdf
>> 
>> The scales are still weird.
>> 
>> The neomorph bone between the orbits is nothing more than the ascending 
>> process of the premaxilla.
>> 
>> For those who still think you have to stare at a specimen in person to 
>> publish on it, well, now you see how that can prove to be a wee bit myopic.
>> 
>> David Peters
>> 
>> Refs:
>> 
>> Cheng, Y.-N., X.-C. Wu, T. Sato. 2007. A new thalattosaurian (Reptilia: 
>> Diapsida) from the Upper Triassic of Guizhou, China. Vert PalAsiatica 45: 
>> 246-260.
>> 
>> Nesbitt, S. J., M. R. Stocker, B. J. Small and A. Downs. 2009. The osteology 
>> and relationships of Vancleavea campi (Reptilia: Archosauriformes). 
>> Zoological Journal of the Linnaean Society 157, 814-864.
>> 
>> Parker, W G. & Barton, B. J. 2008. New Information on the Upper Triassic 
>> archosauriform Vancleavea campi based on new material from the Chinle 
>> Formation of Arizona. Palaeontologia Electronica 11 (3); 14A: 20p.
>> 
>> Wu, X.-C., Y.-N. Cheng, T. Sato and H.-Y. Shan. 2009. Miodentosaurus brevis 
>> Cheng 2007 (Diapsida; Thalattosauria): Its postcranial skeleton and 
>> phylogenetic relationships. Vertebrata PalAsiatica 47:1-20.
>> 
>                                         
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