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An open letter to Dr. David Unwin on pterosaur origins



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