Pterosaurs, prolacertiforms and Peters

[Unwin <h0662eka@rz.hu-berlin.de>]

Regarding Peters recent comments on the relationships of pterosaurs to 
other diapsids. 


Peters wrote:

>After discussing some of the current pterosaur origin hypotheses, D.Unwin 
>(2003) wrote: 'At present, it is not clear which, if any, of these hypotheses 
>is correct. Happily, however, with regard to the polarization of characters 
>used for establishing ingroup relationships with pterosaurs, this is largely 
>irrelevant, because pterosaur skeletal anatomy is so derived that in almost 
all 
>cases the plesiomorphic condition is common to each of the three outgroups 
used 
>in this study: basal ornithodirans, basal archosaurifors and 
>prolacertiforms.'

>Clearly D. Unwin did not want to invite the higher prolacertiforms to his 
>matrix. 


Then he wrote:

>I did not attempt to check characters among ornithodirans or basal 
>archosauriforms mostly because I'm not paid by their lobby and previous 
>experience has taught me that they are not germane to the issue. Also, 
whether 
>the results change or not with these changes is irrelevant to this 
discussion. 
>Also, I have not combed the rest of the cladogram as I have the "outgroup". 
So 
>whether the rest of the cladogram is spotless or similarly corrupt is unknown 
>to me at present.


And later he wrote:

>Precision will make or break a cladogram. As one of the keepers of the 
>pterosaur torch, Dr. Unwin needs to be more precise. Pterosaurs are not 
>orphans. They belong to the Prolacertiformes. They are not 'so derived' 
>from ancestral forms. Pterosaurs are baby longisquamids with minor 
>modifications.


Two comments. 

First, merely because a single analysis produced cladograms in which 
pterosaurs were paired with one or more prolacertiforms does not, in my 
opinion, mean that we should immediately accept this as the gospel truth 
and abandon any attempt to critically test this idea, or explore other 
possibilities. And, as an aside, we should be very wary of the kind of 
dogmatic statements that appear in the last two sentences of the final 
quote. 

Second, two of my colleagues have done exactly that which Peters has 
frequently exhorted us to do - carried out a detailed study of his 
'pterosaurs are prolacertiforms' analysis. The results of this work 
should be published later this year and, as I have mentioned before - 
with full permission from the authors - although they used the same data 
as that presented by Peters they do not support Peters findings. This 
does NOT mean that pterosaurs were definitely not related to 
prolacertiforms - all it means is that, when thoroughly investigated, the 
data presented by Peters does not support this idea. I shall therefore be 
sticking to what I believe to be the most precise statement it is 
possible to make at present about pterosaur origins: 'there are several 
options available and not one of these is more clearly preferable than 
any of the others'. Coding cladistic data sets for the ingroup 
relationships of pterosaurs on the basis of only one of these hypotheses 
(be it prolacertiforms, ornithodirans, or basal archosaurs) would be a 
mistake. 

Cheers,

Dave