An open letter to Dr. David Unwin on pterosaur origins

[David Peters <davidrpeters@earthlink.net>]

Dear Dr. Unwin,

You are a powerful voice in the paleontological community. Editors  
listen to you. Colleagues quote you. You sit on panels. You review  
manuscripts. You travel the world. You've seen dozens of specimens.  
And you have written extensively on pterosaurs.

I was simply wondering, since the topic came up, in the case of  
pterosaur origins, what are you looking for in a pterosaur ancestor?  
Perhaps you haven't found it yet, but what would make you happy that  
you finally have a good candidate?

Would it be a sprawling lizard-like archosaur with an elongated digit  
IV as Wild imagined?

Is it a sister taxon to Proterosuchus and Erythrosuchus, as Bennett  
hypothesized?

Is it a dinosaur-like, Scleromochlus-like quadruped as Benton,  
Gauthier and others understand it to be?

Is it a sister taxon to Sharovipteryx, as you once suggested, then  
rejected?

Yesterday you wrote: "Hone and Benton reanalyse and reject the  
conclusions of Bennett 1996 and Peters 2000, and go with the current  
orthodoxy that pterosaurs are 'derived archosaurs' by which I suppose  
they mean ornithodirans." Since you were mentioned in the  
acknowledgements, can I suppose that means some sort of at least  
vague agreement here? If not, why permit a paper to be published with  
such a vague, poorly supported and unoriginal conclusion?

You also mentioned: "Renesto and Binelli (2006) in Riv. Ital. Pal.  
Strat. on Vallesaurus concluded that pterosaurs grouped with  
Drepanosauridae, and that this clade was located between basal  
archosaurs and protorosaurs (Prolacertiformes). Topographically  
speaking this is only one step away from Bennett's hypothesis (but  
not Peters 2000? hello??) and also corresponds quite closely to the  
ideas espoused in The Pterosaurs." Ahem. This seems to contradict the  
rejections of Hone and Benton mentioned above.

For 7 years you've said pterosaurs cannot be the acme of the clade  
that contains Macrocnemus > Cosesaurus > Sharovipteryx > Longisquama  
(Peters 2000). In 2006 you felt this hypothesis had so little merit  
that you omitted any mention of it in your extensive and otherwise  
inclusive reference list.

You've run many cladistic analyses. Have you tested any of the above  
scenarios against each other to see which is the most parsimonious?  
Wouldn't it be neat to find out?

I'm hoping we can count on your unbiased scientific knowledge and  
insight to bless one of the above hypotheses and provide REASONS why  
one is superior to each of the others. After all, if one can create a  
cladogram with a trout, a lungfish and a cow, we certainly should be  
able to find one or two candidates out there among the entire Amniota  
that would be, if not the ideal sister taxon, still a better  
candidate than any other taxon.

In 2006 you wrote: "paleontologists don't really know where this  
group should sit within the diapsid family tree." And later, " they  
do not fit comfortably in any of the positions on offer." And still  
later, "a temporary dwelling... between the archosauriforms and the  
prolacertiforms (where, by the way there are no mesotarsal ankles or  
arboreal forms)."

An inclusive cladogram would show you, or at least point the way, as  
I tested and showed in 2000.

And if its not the Macrocnemus > Longisquama clade, then can we  
assume that the various apparent synapomorphies found in various  
members of that clade -- including the elongated naris, antorbital  
fenestra, multi-cusped teeth, elongated cervical ribs, deep dorsal  
ribs, high sacral count, attenuated caudal series, elongated scapula,  
tall coracoid, sternal complex (sternum + keeled interclavicle +  
clavicles), magnified deltopectoral crest, migrated centrale,  
elongated fourth finger, reduced fifth finger, elongated ilium, fused  
ischium+pubis, prepubis, sprawling femora, attenuated fibula,  
mesotarsal ankle, elongated lateral toe, and uropatagia -- are ALL  
convergent with pterosaurs?

Isn't it time to take the mystery out of this?

And if not you? Who can we ask who is a greater authority?

Seriously, can you be content NOT to run the analysis and tell us  
your conclusions?

David Peters
St. Louis