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Re: Climbiing Dinosaurs (RE: a little background)




> Mike Skrepnick wrote:
>
> > It seems to me that in combination, the plane of the ungual on pedal
> > digit two ( offset medially ) for that modified "climbing lumberjack"
> > movement,
>
> Just a few very quick thoughts...  In support of this, seriemas have been
> reported to apply their enlarged inner toe claws for tree-climbing - as
> mentioned a few times on this list.
>
> > along with retroverted pubes (reorientation of attachment for hindlimb
> > adductors)
> Is this the same as Chatterjee's explanation for the retroverted pubis in
> "proto-dromaeosaurs" (i.e. pro-avians)?

I'm not familiar with Sankar's view on this, but if the pubis is not
retroverted for the expansion in the gut (as "loosely" is the case in
ornithischians) which is not necessary in various members of  the theropoda,
there has to be some other functional reason for the modification.  Since
the change in anatomy impacts the origin / insertion points of the hindlimb
musculature and therefore to some degree range of motion, etc. . . I don't
think it's unreasonable to assume that this may be a reflection of the kind
of lifestyle implied. What's interesting to consider is whether this
adaptation is strictly applied to hunting / killing techniques or whether it
has earlier origins in "semi arboreal" habitation.  I sometimes wonder if
the ideas like pedal digit modification can be so entrenched in the mindset
of the "paleontological collective" over time, that it just becomes harder
to accept the possibility of other secondary ( but not insignificant )
functions and behaviours attributable to any particular advanced anatomical
characteristic.

> > So really then, all the work in tree climbing
> > dromaeosaurs is done through leg propulsion with the arms and tail
> > secondarily helping in manoeverability, in more lateral movements onto
> > tree limbs, etc...  The only thing that appears to me to be slightly
> > problematic is moving its body and tail through more densely limbed
> > conifers, if they attempted that.
>
> The above objections pertain to trunk-climbing - sort of like the way
> Pacific islanders climb up palms to reach the coconuts at the top.
However,
> what if little eumaniraptorans were adapted to branch-climbing instead -
> using branches for handholds and footholds in a hoatzin-like fashion when
> ascending trees, rather than straddling the trunk.

Exactly so.  Maybe there are a many different applications for certain
anatomical features that are predicated upon stage of growth, size range of
species, variability between species, niche partitioning and environmental
considerations and on and on.  Considering the fossil record gives us so
little information to go on in comparison to the staggering amount of
changes carried over millions of years of time, I think we're a long way off
from having any kind of real understanding of how past biotas functioned.

In the same breath, I think we are often very "limiting" in the amount of
versatility we assign to mechanical form and function within the Dinosauria.
As is often the case ( and has been mentioned in numerous past examples
within the DML) animals are often capable of AMAZING feats of physical
dexterity and complex movements coupled with extended range of motion,
beyond what we might normally ascribe to them based on skeletal evidence
alone.  Although the skeletal remains of dinosaurs pulled from the earth,
are more often than not extremely brittle, the same can't be said for them
in life.  I can't imagine even the largest dinosaurs evolving over millions
of years into a "mobility challenged" state followed by trauma and death. As
far as I'm aware, it seems that most often extinction is brought on by the
appearance of something (not necessarily) bigger or better (smarter?), or by
disease, or climate and environmental change, or by something outside itself
and beyond its capability to accomodate to.  I'm positive Tyrannosaurus was
incapable of doing a backflip, but I'm not ready to rule out a pirouette or
two or an occasional bit of "soft shoe". . . :o)

Mike Skrepnick



> Tim
>
>
> ------------------------------------------------------------
>
> Timothy J. Williams
>
> USDA-ARS Researcher
> Agronomy Hall
> Iowa State University
> Ames IA 50014
>
> Phone: 515 294 9233
> Fax:   515 294 3163