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Re: Wukongopterus, Darwinopterus and Character Selection
Lots of hot air in there...
What happened, Jaime? When you were dealing with specifics we had something to
talk about and agree upon.
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.
> Jaime A. Headden
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