Re: Ornithodira, breathing with long necks

["David Marjanovic" <david.marjanovic@gmx.at>]

> >"Primitive", hm, I'd rather say the ability to fall into torpor is a
> >secondary adaptation in e. g. hummingbirds as well as in e.g. bats and
> >hibernating mammals -- and what are "primitive" birds? Ratites?<
>
> I misspoke. I wasn't implying primitive in a modern sense. I was refering
to
> avian, as in living birds, and "primitive avian" to refer to the metabolic
> regulatory systems in more basal avians (that, apparently, bone histology
> suggests was lower but active.) I should have made myself a little more
> clear. Also, this would make sense, since apparently ectothermic muscles
are
> more efficient, and it would be benificial for an animal attempting to fly
> to have the most efficient muscles available. Is this making sense, or am
I
> being unclear?

Thanks, this is clear to me now. It would make sense, but IMHO you've fallen
into the trap called "Ruben's ectothermic *Archaeopteryx*". Ectothermic
muscles are more efficient in tiring anaerobic exertion, which they can
sustain longer (twice as long AFAIK) than endothermic muscles. In long-term
aerobic exertion, however, endothermic muscles are in advantage. Someone has
calculated somewhere :-] (I think a ref was posted onlist?) that an
*Archaeopteryx* with ectothermic flight muscles weighing a guessed 7 % of
its body weight would have needed to rest for _an hour_ after, IIRC, a
_second_ of flight. B-) "Do you expect me to fly?" -- "NO, Mr. Archie! I
expect you to _DIE_!!!"
        Anyway, considering the fact that *Archaeopteryx* and all birds for
which feathers are known are insulated all over their bodies, none of them
can possibly have been ectothermic, because insulation restricts heat
exchange with the environment.
        About bones... some people think that enantiornithines were
ectothermic because of the LAGs (lines of arrested growth) in their bones.
This conclusion has turned out to be nonsense, at least in hadrosaurs. I'm
sure this has been discussed ad nauseam onlist; if you want, I can dig up
some papers on this subject.