[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: smallest pteros

----- Original Message -----
From: "david peters" <davidrpeters@earthlink.net>
Sent: Wednesday, October 20, 2004 11:31 PM

> I can only repeat: Cladistics is _fundamentally incapable_ of telling you
> a specimen is adult or not. If you put a definite baby into your matrix,
> you think PAUP* would spit it out??? Instead it would show up in all
> 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.]

"All trees" means "all trees that can be generated from the matrix", "all
mathematically possible combinations of the taxa in the matrix".

> If you scored adult and baby chimps, and humans, for snout length,
> 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!

To the contrary -- I've carefully chosen which characters to exclude, not
which to include.

> And you've limited the number of characters to a mere few.

Not necessarily.

> Parents and offspring will be similar!

Similar, yes -- but still not necessarily sistergroups.

> 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.]

There are no large morphological matrices of great apes -- I've seen only
one matrix at all, and it's quite small --, and I'm not going to make one
myself, because this would be about as much work for me as a master's

On the other hand, the number of characters in your matrix that are probably
size- and/or ontogeny-related is huge.

> 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.]

I'm not -- except if you show that hyperprecociality were for some reason

> 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.]

This doesn't necessitate complete ossification -- and as you say yourself,
it doesn't necessitate the ability to fly.

> 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.]

The changed bone histology would still show up. Besides, what happens with
that hormone dose? All sorts of proportions change.

> > >>>>> 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]

I ask because you seem to assume a priori that every fossil pterosaur is
adult unless shown otherwise.

> > >>> 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
> correct size?
> I don't think size is so critical if the egg has a soft shell -- as seems
> 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.]

If it's soft, it's compressible -- the pelvis still has to be large enough,
but "large enough" is much smaller than otherwise!

> > 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
> some of whose properties are encoded in the matrix. Don't interpret too
> 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]

The alternative is to say "I don't know". Wait -- "alternative" is wrong!!!
There are things that a cladogram _cannot_ tell you. To claim that it tells
them when it doesn't is unscientific. I stay with science; you go _beyond_
it by assuming a priori that all characters in your matrix are neither size-
nor ontogeny-related.

> > 2. why do some tiny pterosaurs (Mesadactylus and Nyctosaurus gracilis,
> 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.]

*Mesadactylus* had at least 40 cm wingspan, according to your
reconstruction -- or very short 4th fingers. So I'll say it most certainly
was adult, while *Arthurdactylus* was not. Where can I find *N. gracilis*?
http://www.pterosaurinfo.com/nyctosaurus.html doesn't mention it, at least.

> > 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
> 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
> 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.]

It is everything but a parsimonious assumption that your matrix includes all
pterosaurs that existed. _This_ is what _should_ give us one single MPT.

> [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

We've got some. Padian, Horner & de Ricqlès cut some up.

> > 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
> 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]

*Eudimorphodon cromptonellus* has been (it's not complete). It has been
found to be neither a hatchling nor an adult. It was still growing at larger
than adult rates.