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Re: What is biomechanics? (not so long)



----- Original Message -----
From: "Colin McHenry" <cmchenry@westserv.net.au>
Sent: Friday, September 20, 2002 4:52 PM
Subject: What is biomechanics? (or, The Truth About Flying Snakes - Was: Re:
science and philosophy)


> RECONSTRUCTING EVOLUTIONARY TRANSFORMATIONS USING BIOMECHANICS
> Take, for example, the method developed by the Senckenberg crowd,
> Kronstruktionsmorpholgie.

Do they happen to publish in Senckenbergiana Lethaea (available in the
geosciences library)? In that case I could read and translate the papers.

> An important part of Kronstruktionsmorphologie is the mapping of
> biomechanically viable transformation pathways across a series of
different
> 'Konstruktions' (organisms with differing bodyplans).  [...]
> You take your Kronstruktions and then you work out which
> transformations from one Kronstruktion to another are biomechanically
viable
> without compromising the integrity of the organism.  Usually you'll end up
> with a shortlist of possible transformations - A can transform into B, and
B
> can transform into C, but C cannot be derived directly from A).

Sounds like a good idea. Should be done. But exactly what transformations
are "biomechanically viable" will often be subjective, and
Konstruktionsmorphologen might in some cases reveal more about how vivid
their fantasy is than about what could really have happened.

"It is notable that one of the strongest argument in [...] [a paper that
tries to destroy Ecdysozoa and to save good old Articulata] in favour of
their character interpretation is a character's ability/inability to take
part in an evolutionary scenario. The 'Kiplingesque' stories are going back
to their prephylogenetic position: to represent the primary tracks of
phylogeny, identified prior to analysis. According to [...] [same paper],
the arthropods have to be related to annelids because the derivation of the
arthropod body form [Konstruktion...] from the annelid-like one appears to
be more easily imaginable than from the priapulid-like morphology. _Any
possible_ [italics] phylogenetic pattern can be 'reconstructed' if one uses
his/her personal imagination, or its lack, as a proof. The difficulties with
the creation of the ecdysozoan-panarthropod scenario imply only that the
Ecdysozoa hypothesis is less intuitive, but not necessarily incorrect.
    Nonetheless, the problem of derivation of the panarthropod body form
[...] from the *Priapulus*-like morphology, should not be neglected, and,
indeed, it is _not_ neglected by, for example, [...] [4 refs]. Nobody
seriously suggests 'arthropods evolving from nematode-like ancestors' as
[...] claim -- the nematodes are evidently highly derived and structurally
simplified members of the Ecdysozoa [...]"

p. 161 of
J[an] Zrzavý: Ecdysozoa versus Articulata: clades, artifacts, prejudices, J.
Zool. Syst. Evol. Research = Zeitschrift für zoologische Systematik und
Evolutionsforschung 39, 159 -- 163 (2001)

> CAN KONSTRUKTIONSMORPHOLOGIE SAVE DINOBIRDS?
> What I find hard to understand is why this is so seldom done (at least, as
> far as I can tell).

Very simple -- because the papers are in German.

> The biomechanical implications of this transition are
> huge - the ability to fly should leave biomechanical signatures all over
the
> anatomy of an ancestral bird as compared with non-flying forms,

Actually not. The necessary features should accumulate more or less one by
one, and when enough are present, flight becomes possible, and selection can
work to refine the flight apparatus.

> To me, as a clado-skeptic, the confusion about the origin of birds
strongly
> supports the contention that cladistics on its own can tell you very
little
> of consequence.  If cladistics was the be-all-and-end-all of phylogenetic
> analysis then why hasn't there been a definitive answer to the question of
> what animals birds evolved from.  It's not as if you're short of fossils,
is
> it?

Sure it is. What is flooding us now is largely or entirely Early
Cretaceous -- too late. Therefore the definitive answer isn't more specific
yet than that birds are coelurosaurs (though at the moment there's a very
broad consensus that Troodontidae and Dromaeosauridae are part of the
sistergroup of birds incl. *Archaeopteryx*).

> DON"T FORGET BODY SIZE AS A BIOMECHANICAL PROPERTY
> As for 'ground-up' vs. 'tree-down', well, from an outsider's point of view
> (I usually skip these posts, so if I've got the wrong end of the stick I
> apologise) I am midly surprised that this is still an issue.  Whatever the
> protobirds evolved from, and whenever they did it, it seems to me far
easier
> to derive a bird from a small, aboreal animal than from a medium sized
> cursorial one.

In the absence of ascertained underwater fliers (and that'll likely continue
for quite some while), what about a tiny generalist-subcursorial one like
*Microraptor*... the arms of this specific form are all wrong, and the tail
is already stiffened like in dromaeosaurids, but the rest is damn close to
*Archaeopteryx*, just smaller.

> And for those who might support an aboreal
> origin of birds, I would suggest (for what it's worth) that a small animal
> is going to be able to be aboreal without necessarily showing any of the
> specialist anatomical features required by an larger climbing beast, so
any
> anatomical indicators related to climbing ability may be very subtle
indeed.

Sure.

> Surely no-one on this list
> believes evolution is parsimonious?  If you don't believe in it, why use
it?

Surely no-one on this list believes evolution is maximally munificent...
after all, we haven't seen a hopeful monster so far. Therefore parsimony is
the best place to start. At least. I do think it's a good thing what the
authors of *Rahona(vis)* did: they presented the MPT and a tree that was one
step less parsimonious, for the reader to choose. I also think the more
fossils we have and include in the character matrix the more likely is the
MPT to be true.

> Okay, Jaime then said;
> >Feathers, as
> >comparative tests show, do not make an animal fly, even a bird.
>
> But no-one said that feathers alone make the foul.  Did they?

Some said it had big wings and therefore should have been a flier. And the
argument is that if it had big wings (and the feathers didn't attach to the
legs), then it's probable but by no means certain it was actually able to
fly: "Remiges, as comparative tests show..." I think that was meant.

> [...] Konstruktionsmorphologie - at least how I understand
> it at the moment.  The problem with this is that the
> relevant literature is largely in German, which I don't read.

That is the dilemma. Neither has English got into the position Latin once
had, nor do the majority of scientists whose mother tongue is English learn
any foreign language -- and those folks are the majority of scientists in
the world, and the vast majority of scientists with actual grant money. The
older generations of most other scientists are often bad at English, so the
information flow doesn't work well in the reverse direction either. For
example, I'm under the impression that many German cladists -- of those
AFAIK rather few that there are -- don't use character matrices and computer
programs, weight intuitively and use parsimony very little.