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Re: Pterosaurs and birds, was Re: birds and pterosaurs




--- Michael Habib <mhabib5@jhmi.edu> wrote:

> > In theory, evolution might bypass the problem in
> that
> > bird with extremely large wingspan has long flesh
> part
> > of hand, but flight-feathers remain at manageable
> > size.
> 
> If you mean the arm itself is longer, then yes.  

Agreed.

> > Judging that big pterosaurs are more common than
> > equally big birds, pterosaurs could grow bigger on
> > similar amount of food.
> 
> Are you thinking there is a metabolic difference
> then?  

Yes, but not difference in general body metabolism,
but in energy and specific aminoacids dedicated to
form flight feathers.

Large soaring bird needs to gather lots of energy and
aminoacids to keep its flight feathers growing, while
has wing surface is damaged by feather loss. Very big
bird requires high density/accessibility of prey to
make ends meet. 

At some point, there is no ecosystem with sufficent
numbers of big surface feeding fish (or megafauna
carrion) for such a bird to evolve.
 
However, 
> large size is an advantage in soaring flight in many
> ways, and there 
> isn't actually anything to suggest that teratorns or
> pseudodontorns 
> would have been poor foragers. 

Agreed. I am not talking about flight speed, agility
etc., but about energy and metabolic demands.

> flight, or pelagic 
> food resources may have been readily available (but
> see below).  

Possibly abundance of large shallow seas in Mesozoic 
also contributed to diversity of large pterosaurs. 

However, at least Quetzalosaurus is interpreted as
inland form.

> efficient flyers, one way or the other.  And yes,
> mechanical 
> constraints do seem to differ such that pterosaurs
> generated more 
> large-bodied flyers than birds, but this is not the
> same as being 'more 
> efficient' or 'less restricted' (I suspect it was
> partially to do with 
> the relatively lower wing loadings of pterosaurs per
> unit mass.)

I think a paleontologist may not be accustomed to
think that physical efficency of animal is relative to
it's ecological niche. 

Very large bird might be inefficent, but will evolve
and live when more efficent pterosaurs are extinct.
Their ecological niche may be restricted, but if there
are very food-rich conditions, they will evolve. 
 
> > 10mm/day, but full moult of vultures and pelicans
> > takes 3-4 years.
> >
> 
> Thanks for the snippet; that's very interesting.  I
> wonder why the molt 
> is so slow in those groups...

Because soaring bird can lose only few feathers at a
time. With slow speed of growth, big feather length,
many feathers - the cycle of replacement becomes long.



        
                
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