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Re: pterosaur stuff

re: pterosaur stuff(The original was in HTML, so I don't know if it even
arrived in the archives. Therefore I haven't deleted anything in the

----- Original Message -----
From: David Peters
To: dinosaur@usc.edu; david.marjanovic@gmx.at
Sent: Thursday, September 23, 2004 9:19 PM
Subject: re: pterosaur stuff

> David Marjanovic wrote:
> PAUP*, or cladistics in general for that matter, is completely _incapable_
from telling you if a character is ontogenetic variation. If you have adults
and juveniles of the same species in a matrix, there's not even a guarantee
that they'll turn out as sistergroups (chimp babies would probably cluster
with adult humans instead of with adult chimps).         To put it in
impolite terms, Feduccia is completely right in that _if_ you put garbage
in, you get garbage out of cladistics.
> I might agree with you, if we were talking about a few characters. The
drawings at pterosaurinfo.com were created after the cladogram was finished.
It's graphic shorthand. Easy to understand.
> This cladogram uses 182 characters. How many is enough to override the
GIGO roadblock? Give me a number.

I could only give you a proportion (50 % plus one character, in an ideal
case). I can't give you a number because I don't know how many size-related
and ontogeny-related characters -- potentially as well as known to be
such -- there are in your matrix. Could you send me that matrix, please? I
can't comment it before October 9th, though -- too many exams until then.

> If there is no number high enough, then science, as it stands now using
PAUP, can't answer your question.

_Cladistics can't. This is true._ Science in general can, however -- by
studying the ontogeny of other vertebrates. Immature bone texture, badly
ossified articular ends, badly or not ossified carpals/tarsals/small
phalanges (already mentioned in Wellnhofer's encyclopedia!), short distal
limb elements, short tail, big head, short snout, big eyes... arranged in +-
decreasing order of certainty with which they indicate immaturity.

> And what make you think there is garbage in the data? That is a
prejudicial statement.

No. The fact that you put hatchlings in your matrix in the first place is
not a good idea. I would never put "*Liaoxiornis*" in my bird matrix; all
its "diagnostic" characters are, with varying but high degrees of certainty,
related to the ontogenetic age of the specimens.

> A scientist would say, let me see and test your data before I return a
verdict. What you have offered is cocktail chatter.

No, science. I apologize for having made you aggressive, but you still
haven't brought up evidence that the specimens in question are really adult.
It's you who's making the extraordinary claim here.

> Finally, let's go back to Scaphognathus.  If you're convinced No. 9 is a
juvenile, why isn't it a juvenile Scaphognathus -

I will readily admit that I don't know enough about pterosaurs to tell this.
However, it does look pterodactyloid. It lacks a long tail (...though if the
tail is there at all, it's hidden beneath matrix); I can't see a long 5th
toe; the neck seems to be attached to the ventral side of the occiput
instead of to the caudal side; and the metacarpals are fairly long.

> one in which the tail is not quite ossified and the antebrachium hasn't
quite caught up with the metacarpus?

Why should the metacarpus elongate before the antebrachium? Why should a
long, unossified tail exist at all? (Note that the rest of the animal is
ossified as far as the resolution of the pic lets one tell. A
"rhamphorhynchoid" tail is supposed to be very stiff -- what is the point of
making it of pliable cartilage when the animal is already using it?)

I see only one reason for assuming No. 9 were adult: its babies
http://www.pterosaurinfo.com/no9_insitu_babies.html. Well, you must have
used a higher-resolution photo; many of the details in the mouseover (e. g.
the teeth of the head ?under? the abdomen of No. 9, each about 3 pixels in
area) are impossible to find in the original. But even if they are real -- 
and I still think they're just faces and pyramids on Mars --, nobody says
they have to be the offspring of No. 9. You have yourself written that you
find pterosaur breeding grounds littered with babies everywhere.

> Le'ts roll up our sleeves and figure this one out together!

Oh yes.

> And enough analogies about your brother.

Why? Tetrapod ontogeny is tetrapod ontogeny -- in *Diplocaulus* just as well
as in *Homo*.