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Re: An open letter to Dr. David Unwin on pterosaur origins



----- Original Message ----- From: "David Peters" <davidrpeters@earthlink.net>
Sent: Friday, May 18, 2007 7:32 AM


I was simply wondering, since the topic came up, in the case of
pterosaur origins, what are you looking for in a pterosaur ancestor?

Ancestor? We have almost no chances of finding an ancestor, and none of securely recognizing it as such if we find it. So we're looking for the sister-group of Pterosauria. Here it's obvious what we're looking for: derived characters shared with Pterosauria but not with the next two more distant outgroups.


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

The other way around. We can't know which of the many autapomorphies of the pterosaurs will be present in their sister-group once we identify it and which won't.


For 7 years you've said pterosaurs cannot be the acme of the clade
that contains Macrocnemus > Cosesaurus > Sharovipteryx >
Longisquama (Peters 2000).

Taken literally, there's of course a good reason for that: "acme" and "clade" contradict each other.


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?

Wouldn't it be neat to have unlimited time and travel grants? Be a bit more patient.


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

That was way back when you didn't even know how to order characters, let alone how to avoid the effects of correlated characters (including those correlated to size and/or ontogeny). Look, I'm not blaming you for not having had a manual of PAUP* or an introduction into cladistic analysis, or for not having immediately solved the often very difficult problem of correlated characters; I blame you for not having asked anyone even the most obvious questions.


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?

Cladistic analysis will tell us whether they are convergent or not. That's not something to assume.