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Re: Is there something which limits large size in neornithean birds?



On Thu, Mar 15th, 2012 at 12:46 PM, Augusto Haro <augustoharo@gmail.com> wrote:

> Dear all:
> I was thinking why no neornithean attained a size in excess of 500 kg
> (half a metric ton), whereas other coelurosaurs did. If pneumaticity
> helps achieving large sizes, neornitheans may have advantage even over
> most other dinosaurs.
> Have some cause been proposed to explain this? Perhaps the horizontal
> femur cannot avoid breaking up at large sizes? Perhaps the fast, and
> especially determinate growth is a disadvantage (for attaining large
> size) compared with animals with indeterminate growth? Why didn't
> large Cenozoic birds grow enough to fill the space left by sauropods?

Perhaps the shift away from the r-strategy of their ancestors has doomed birds 
to a maximum size 
due to the maximum size an avian egg can be and still be viable? Most birds 
directly incubate their 
eggs, so perhaps the shell thickness of a few large eggs (rather than many very 
small eggs) would 
need to be thicker than efficient gas exchange would allow for incubators 
greater than half a tonne 
in mass.

The lack of a counter-balancing bony tail might also inhibit bipedal locomotion 
at very large avian 
sizes.

-- 
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Dann Pigdon
Spatial Data Analyst               Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj
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