[Odonata-l] Oxygen and insect gigantism

[Richard Rowe]

Nick and Ailsa Donnelly wrote:
> This is getting philosophical.  I believe excess Permian oxygen is not the
> answer, as I have said.  A scale-up of 4X requires a lot of thought.  Let's
> try a thought problem.  Suppose that the largest birstd extant were
> sparrows, and that we investigated the phisiological scanilg in the range of
> hummingbirds to sparrows.  Then someone finds a fossil condor.  How can that
> be? Everyone asks.  If we look at sparrow phisiology then we see that we
> can't scale this up to condor size.  But somehow exactly this did happen.  '
>
> I suppose that if the larger members of a group become extinct for whatever
> reason (I suggest predation for dragonflies, plus the evident physiological
> demands for eating and growth of the laregr forms), then it should follow
> that the successful, relatively diminutive descdants will not necessarily
> retain sufficient physiological potential to be "re-scaled" to the previous
> large size.
>
> When you have a range of observations, it is never satisfactory to scale
> beyond your observable limits.
>
> Nick Donnelly
>   

Hear, hear ...

Wrt extinction, they may also have been undermined from below. If large 
herbivores were out-competed by fast-developing masses of smaller 
insects then there would be no niche left for large dragonflies ... 
speculation, but in biology it isn't necessarily direct.

The beetle leg scaling is irrelevant. It could be argued that if legs 
had to accommodate trachea then they would scale appropriately.  It is 
the efficiency of trachea that allows the legs to 'shrink' while 
remaining metabolically active,

Richard

-- 
Dr Richard Rowe
Zoology & Tropical Ecology
School of Marine & Tropical Biology
James Cook University
Townsville 4811
AUSTRALIA

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