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Re: Wukongopterus, Darwinopterus and Character Selection



Whew...

Lots of hot air in there...

What happened, Jaime? When you were dealing with specifics we had something to 
talk about and agree upon. 

David P

On Nov 27, 2009, at 3:39 PM, Jaime Headden wrote:

> 
>   It should be noted in this debate that of all of these taxa, several 
> methodological processes seem to either be glossed over, ignored, or simply 
> not arrived at conciously. The addition of further distinguishing features 
> should help to clarify the nature of whether any of these taxa form a clade 
> together, are a gradational transition between two other morphotypical 
> grades, both, or they are convergent upon one another but not actually allied 
> taxa; but also there being further added taxa, the prevention of the 
> exclusion of taxa which are not safely removable from the matrix, etc., and 
> removal of characters or states which only come up as autapomorphic features 
> of some taxa.
> 
>   With regards to the bulk of these issues, increased taxonomic samplin and 
> character samplin cannot hurt, but only benefit it and further research. 
> Reducing the sampling or representation of taxa or characters, while at the 
> same time oversampling limited regions of anatomy, results in an unrealistic 
> process in phylogenetic study. The taxa in question require us to sample 
> speculatively but also frugally, being wary of the trap of just dumping any 
> old character we think is there into the matrix. In a morphological matrix, 
> it is the sharing of characters that counts, rather than the possession of a 
> unique set of features (unlike a taxonomic diagnosis!) and this makes the 
> argument for the uniqueness of a taxon being tested in a matrix untenable.
> 
>   No matter the number of features that *Wukongopterus* can be said to differ 
> from *Darwinopterus* with, this is meaningless without context, and only 
> those features which are shared between *Wukongopterus* & any other pterosaur 
> (and similarly *Darwinopterus* and any other pterosaur) actually matter in a 
> phylogenetic analysis. We can say with some definition that these two taxa do 
> differ, but by how much is unclear (yet), but moreover that these two taxa 
> suggest that the transition from "rhamphorhynchoid" to "pterodactyloid"* 
> morphotypes is even more complex than is suggested by Lü et al., and that if 
> any one taxon can attain this morphology, then one could argue two of them 
> could, producing two convergent lineages. It would be difficult to test this 
> because of the state of cladstic matrices favor grouping taxa, and even 
> convergent features require additional signals to counteract. The dentition 
> in these trwo taxa differ enough to suggest that there is a trend toward two 
> different "pterodactyloid" morphologies: *Wukongopterus* teeth are similar to 
> those of some ornithocheiroids like *Tropeognathus mesembrinus*, 
> *Istiodactylus latidens*, or *Pterodactylus antiquus*, including posessing a 
> constricted base of the crown, while *Darwinopterus* resembles *Anhanguera 
> santanae* and *Cearadactylus atrox*.
> 
>   One could further argue that the variations in cranial/dental morphology 
> are themselves convergent, while the postcrania are conserved, and dietary 
> similarities would force variation that would converge one one another, such 
> that *Darwinopterus* and *Wukongopterus* can be either two different groups 
> that converge on the same "pterodactyloid" morphology, but also two otherwise 
> closely related taxa that each converge on the derived conditions of several 
> other groups. It is not likely without robust cladistic analysis, better 
> sampling, and more thourough examination of the characters themselves, to 
> determinhe which of these is more likely.
> 
> * I should also hope to note that Pterodactyloidea contains more morphotypes 
> than is implied when being compared to the "rhamphorhynchoid" morphotype. On 
> top of the "basal" ctenochasmatoid/pterodactylid morphology, you also have 
> the pteranodontoid, ornithocheiroid, azhdarchoid, dsungaripteroid etc. 
> 
> 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 
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> 
> "Ever since man first left his cave and met a stranger with a different 
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>                                         
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