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Re: Fwd: Polytomy question (and sickle claws)



David wrote:

"On the topic of sickle claws... I still don't
understand how they could be useful in climbing. They
are called "sickle" rather than "hook" because
they have a cutting edge. For climbing I'd expect a
round, if not outright flat, ventral surface that can
carry weight, not just a pointed tip 
alone."

As the folds of hide build up in front of the
"cutting" edge, the hide becomes effectively too thick
to cut. The same thing happens with a knife and deer
hide, unless (or even if) the knife is shaving sharp.
When making long cuts while skinning, the left hand is
used behind the knive to tension the hide, which
prevents folding/buildup, and the knife is angled back
so that the hide rides up on to the blade without
folding.

The "grappling" process as I envision it (w/ the help
of P. Manning et al) goes like this: 1) the claw, _in
the up position_ is driven into the hide w/ a kick. 2)
the claw is then moved into the down position. This
moves the claw semicircularly so that the tip ends up
just underneath the hide, 1 claw length away from the
entrance wound. The hide is now clamped between the
outer toes (outside) and the sickle claw (inside). The
cutting edge is necessary for penetration.

In the climbing process, the claw is left in the up
position w/ the outer toes folded back; kick, step,
kick, step, exactly as a human equipped w/
poleclimbers does it, the difference being the
orientation of the sheer face being climbed, and claws
on the "hands". I think this is slightly different
than the "crampon" analogy used in the Manning paper
in that the claw is in the up position and the claws
of the outer toes are not actively involved. Again,
this would aid in penetration.

Lastly, I feel that Mike Habib's comments relative to
multi-function are imminently reasonable.

Don



--- Jordan Mallon <jordan.mallon@gmail.com> wrote:

> David asked me to forward this...
> 
> --
> Jordan Mallon
> 
> BScH, Carleton University
> Vertebrate Palaeontology & Palaeoecology
> 
> Paleoart website:
> http://www.geocities.com/paleoportfolio/
> http://dino.lm.com/artists/display.php?name=Mallon
> MSN Messenger: j_mallon@hotmail.com
> 
> ---------- Forwarded message ----------
> From: David Marjanovic <david.marjanovic@gmx.at>
> Date: Oct 26, 2005 4:48 PM
> Subject: Re: Polytomy question (and sickle claws)
> To: jordan.mallon@gmail.com
> 
> 
> Could you please forward this to the list? For,
> presumably, some reason
> Listproc seems to annihilate my messages without
> telling anyone. Mickey
> Rowe is investigating.
> 
> ---------------------------------
> 
> > > What I find interesting is that every
> evolutionary
> > > change is always modeled as a split.  How about
> > > species that simply change over time without
> spliting
> > > into two different lineages?  This is rarely
> captured
> > > in any phylogenetic tree.  Is it because of lack
> of
> > > evidence?  Would we know them if we see them
> (not me
> > > of course but you get the point).
> 
> We would not know them if we saw them. We could only
> suspect, more or less
> subjectively.
> 
> If a cladogram shows two taxa as sister-groups, if
> one of them completely
> lacks autapomorphies ( = derived features of its
> own), _and_ if its age
> fits, then it _enters consideration_ for being an
> ancestor of its "sister-
> group".
> 
> However, here we must stop. All we have here is
> negative evidence. We can
> find out that something is _not_ the ancestor of
> something else by finding
> its autapomorphies; we cannot do the opposite. (If
> we don't find
> autapomorphies, this doesn't mean they weren't
> there. We might overlook
> some; more importantly, we cannot find
> autapomorphies that aren't
> preserved.)
> 
> This is not a failure of cladistics, it's a failure
> of science as a whole.
> In other words... if you're talking about late
> Pleistocene diatoms found
> in deep-sea sediments, go ahead assuming you have
> found an ancestor
> because it fits the above criteria; but if you're
> talking about Mesozoic
> vertebrates, I recommend to forget about it. The
> (known) fossil record is
> bad enough that the chances that you've really found
> an ancestor are
> extremely small.
> 
> > The most important thing to remember here is:
> CLADOGRAMS ARE NOT
> > PHYLOGENIES.  They're two different things.
> 
> Well, not quite. Cladograms _are_ hypotheses about
> phylogeny, with the
> additional assumption that none of the OTUs is an
> ancestor of any of the
> others. In many (though clearly not all) cases, this
> assumption is
> reasonable; cladistics was invented by neontologists
> for neontologists
> (Hennig even stated that it should only be used for
> taxa of the same time
> slice, without ever explaining how thick such a
> slice would be allowed to
> be), and most of the fossil record is bad enough
> that we can't expect to
> find an ancestor.
> 
> > Unfortunately, many people seem to miss this point
> and treat the two
> > as the same.  This is a problem that is of special
> interest to me
> > lately, as some of my buddies and myself are
> looking into what we
> > think might be an anagenetic series of mosasaurs
> in the WIS.
> 
> An anagenetic series doesn't need to be an
> unbranched line of ancestors
> and descendants (though it obviously _can_ be). It's
> enough if each branch
> has its autapomorphies in some characters other than
> those which show the
> anagenetic change. In other words, you can't tell a
> phylogeny from a
> pseudophylogeny this way.
> 
> On the topic of sickle claws... I still don't
> understand how they could be
> useful in climbing. They are called "sickle" rather
> than "hook" because
> they have a cutting edge. For climbing I'd expect a
> round, if not outright
> flat, ventral surface that can carry weight, not
> just a pointed tip alone.
> 
> --
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