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re: smallest pteros



D. Marjanovic replied to my queries:

> Is the holotype of P. kochi (No. 23 of Wellnhofer) a juvenile? Or an
adult?

There is evidence -- the proxies I've mentioned, and the plots by Jouve -- 
that it's a juvenile. What evidence is there that says it's adult?

dp [see below]


I can only repeat: Cladistics is _fundamentally incapable_ of telling you if
a specimen is adult or not. If you put a definite baby into your matrix, do
you think PAUP* would spit it out??? Instead it would show up in all trees,
and there is no guarantee that it would cluster with adults of its own
species, because, to varying but not easily predictable extents, ontogeny
recapitulates phylogeny.

dp [show me that a baby 'anything' would show up "in all trees." If you can't 
show me, as I have shown you with a cladogram, then this is only cocktail 
chatter. Not science. Really, David, I'll wait until your exams are over. Or 
send me the refs.]

If you scored adult and baby chimps, and humans, for snout length, relative
head size, relative orbit size, tooth count and a few more characters, and
added this to a primate matrix, the baby chimps would cluster with us
instead of with their parents.

dp [ David, you've fallen into a classic cladistic trap that Unwin, Kellner, 
Senter and many others have likewise fallen into. You've carefully chosen your 
characters!  And you've limited the number of characters to a mere few. What 
you must do instead, and what all future cladograms should do, is to look at 
every body part from rostrum to toe ungual and code as many 'not very carefully 
chosen characters' as possible (say over 150 to be safe) and only then will you 
see that the vast majority of characters in closely related taxa are indeed the 
same! Parents and offspring will be similar! If you do you'll see that baby 
chimps don't have the sort of pelvis, digit proportions,  palate, hair 
distribution and nasal cartilage that baby humans share with their parents. 
Ultimately PAUP will tell you that from a _suite_ of characters the most 
parsimonious tree will indeed match nature's own. Again, if you can prove 
otherwise, do so! We all would like to see this.]

> > In these individuals all skeletal elements
> > of the flight apparatus including the pteroid are ossified and, in
addition
> > to containing structural fibres, the flight membranes were approximately
> > the same shape and proportions as those of the adults.
>
> Are U & D describing adult characters above?

They are describing flight-related characters. If the pteroid is not a
dermal bone (but either an endochondral one -- like a centrale -- or a
tendon ossification), it should ossify _relatively_ late; 

dp [ you're arguing my point! Thank you.]

one should think
that it wouldn't ossify long before the young became flighted, because
before they'd be rather useless.

dp [you (and I) don't know what the young were using their nonvolant wings for, 
but if you watch baby birds you can see that they indeed use their wings to 
communicate their needs long before they can fly with them.]

> > Moreover, critical components of the fore and hind
> > limbs show isometric growth patterns
>
> Are these isometric growth patternsphylogenetic or ontogenetic in nature?



> This is further supported by the discovery of these fossils
> preserved in locations far from any likely nesting site.
>
> >>>> Are U & D leaving the door open to the possibility that they're
looking at adults?

I don't think so. They just mention that the locations are _consistent_ with
the specimens being hyperprecocial juveniles -- they didn't have to be
either adult or clinging to a parent to get there, they just had to be able
to fly. Of course this one sentence doesn't rule out the other two
possibilities.

dp [all you need to change from a precocial juvenile to a fully functioning 
adult is a dose of sex hormone, and that doesn't show up in the fossil record.] 

> >>>>> While the literature labels every tiny pterosaur a juvenile, I
wonder if U & D has tested previous assertions? And if so, what is their
"litmus test"? [see below for questions regarding the currently accepted
"litmus tests" for immaturity]

What is your litmus test for adulthood? The presence of an external
fundamental system?

dp [ not sure, that's why I ask the question of the experts]

> >>> Okay, Dr. Unwin has set a minimum adult wingspan of 40 cm. Which
pterosaur is this? Does it have a pelvis large enough to pass an egg of the
correct size?

I don't think size is so critical if the egg has a soft shell -- as seems to
be the case.

dp [ it's critical. Even if soft. Just think about what pain you'd go through 
passing a 'too large' object through your cloaca.]

> And yes, I'm aware of the various size-independent characters used
previously, but the questions to those tests are:
>
> 1. why in cladistic analylsis do entire clades of pterosaurs (basal
ornithocheirids + cycnorhamphids) appear to be immature using these tests?

Nobody says they really _are_ clades. They could be artefacts of the
inclusion of size- and/or ontogeny-related characters. PAUP* gives you the
shortest trees for your matrix, not necessarily the one for the real animals
some of whose properties are encoded in the matrix. Don't interpret too much
into a cladogram.

dp [and the alternative is??? voodoo? opinion? dogma?  Stay with science, 
David. Cladistics may not be perfect (especially the way some people practice 
it,) but it's the best we have. You're free to disagree, but you better have 
better evidence]

> 2. why do some tiny pterosaurs (Mesadactylus and Nyctosaurus gracilis, for
instance) appear to be mature according to these tests?

Which tests? Bone histology?

dp [ tiny Mesadactylus has a fully fused synsacrum. giant Arthurdactylus does 
not. Tiny N. gracilis has a fused scap coracoid. The larger nyctos do not. 
Something's wrong here.]

> 3. why in cladistic analysis, do the tiny pterosaurs appear at the bases
of major clades and complete the spectrum of pterosaur diversity to create a
single most parsimonious tree?

Because ontogeny recapitulates phylogeny, juveniles often show
plesiomorphies that the adults lack. There are tons of examples. -- As to
why there's a single MPT, this is either a pure coincidence of your matrix,
or you've won in the German lotto (6 out of 49).

dp [as a scientist you should admit that there are other possibilities, more 
parsimonious possibilities. If you were a lawyer I would expect such arguments 
from you. But you can do better! I sent you the file so you could find the 
flaws - for the betterment of science. Now go back and look for the flaws. And 
we can't talk about ptero ontogeny until we get some verifiable juveniles]

> 4. considering the alternative theory for a moment: why should a
'hypothetical' tiny adult pterosaur, hypothetically stunted by a premature
hormone surge (or a phylogenetic series of same over thousands of years),
ever develop 'mature' bone characters when nothing else about them, except
perhaps their hypothetical ability to reproduce, appears to be 'mature'?

If by "bone characters" you mean histological characters, then the answer is
simple: because it (almost or completely) stops growing.

dp [I'm only guessing, but I'll bet the tiny pterosaurs have not been 
histologicall sectioned. Probably because they are usually complete specimens 
and you don't want to ruin them]