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Re: Sifaka and Chukar Behavior: Trees Down or Ground Up?



Dear Ronald, This seems to me to be an extremely
sensible (and well-articulated) position on the trees
down/ground up issue. We evolutionists seem to easily
get ourselves into mental boxes by assigning
behavioral limitations to fossil forms which, although
seemingly predisposed towards a specific adaption,
were possibly capable of other behaviors. The
tree-climbing domestic goats of arid countries in
Africa and the Mediterranean are a good example: who
would ever place these creatures, if known only from
fossils, in this context? If feathers first evolved as
an aid to thermal regulation/conservation, the
aerodynamic shapes we associate with primary and
secondary sets of feathers known from extinct and
living lineages could have evolved more than once in
association with behaviors that were to some extent
already preadapted to both flapping AND
gliding.....Mark Hallett  
--- Ronald Orenstein <ornstn@rogers.com> wrote:
> At 12:47 AM 23/01/03 -0800, Jaime A. Headden wrote:
> >What this appears to be, rather, is that one group
> of small, predatory
> >theropods in the trees became adapted to gliding
> independantly of all
> >other  avian-style theropods, and that in no way do
> these finds support
> >either the trees down or the ground up hypotheses.
> Merely an interesting
> >sideline. The tetrapteryx of Beebe and the
> feathered legs of Feduccia et
> >al. are interesting predictors of four-winged
> animals, but again do not
> >show how flapping flight would have evolved.
> 
> In fact I wonder, given the range of new
> discoveries, whether ANY single 
> fossil discovery can now shed light on this
> question.  What we seem to have 
> is a radiation of feathered or proto-feathered
> dinosaurs that may well have 
> lived a variety of lifestyles in a variety of
> habitats, with their feathers 
> possibly serving a variety of functions.  It may be
> that the adaptive 
> shifts involved occurred rapidly and, evolutionarily
> speaking, fairly 
> easily.  Therefore a finding that one species (or
> another) seems to have 
> been arboreal (or not) may do little more than
> attest to the variety of 
> lifestyles and behaviours taken up by feathered
> dinosaurs.
> 
> Certainly within living birds there are numerous
> examples of 
> closely-related species with quite different
> lifestyles (I have mentioned 
> the flickers (Colaptes) before, which include purely
> terrestrial species 
> confined to treeless areas and highly-arboreal
> forest-dwellers, with 
> intermediates).
> 
> The assumption of this whole debate seems to be that
> there was a very clear 
> dichotomy between terrestrial and arboreal modes of
> life, and that only one 
> of these led to the evolution of flight in living
> birds.  I do not see why 
> this has to be correct - especially if flight or
> near-flight was being 
> achieved repeatedly in a variety of forms.  What,
> for example, does it mean 
> to be arboreal?  There are many birds today that are
> both arboreal and 
> terrestrial; birds (like herons) that are primarily
> terrestrial but nest in 
> trees; others (like some wood warblers) that forage
> in trees but nest on 
> the ground; others (like some grouse) that feed and
> nest on the ground but 
> will fly into trees to escape predators or to roost.
> 
> Why can we not speculate (especially considering
> Dial's work) that 
> pre-flight adaptations may have evolved neither for
> a purely arboreal or a 
> purely terrestrial animal?  Is it possible that
> their chief advantage may 
> have been to allow their bearers the versatility to
> make use of both trees 
> and the ground to varying degrees, for a variety of
> purposes, rather than 
> to enhance one way of life or the other?
> 
> 
> --
> Ronald I. Orenstein                           Phone:
> (905) 820-7886
> International Wildlife Coalition             
> Fax/Modem: (905) 569-0116
> 1825 Shady Creek Court
> Mississauga, Ontario, Canada L5L 3W2         
> mailto:ornstn@rogers.com
>          
> 
> 
> 


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