Wukongopterus, Darwinopterus and Character Selection

[Jaime Headden <qi_leong@hotmail.com>]

  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 
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)
                                          
_________________________________________________________________
Windows 7: It works the way you want. Learn more.
http://www.microsoft.com/Windows/windows-7/default.aspx?ocid=PID24727::T:WLMTAGL:ON:WL:en-US:WWL_WIN_evergreen:112009v2