Re: Warm-Blooded debate

[NJPharris@aol.com]

In a message dated 97-06-20 21:30:03 EDT, Dinogeorge@aol.com writes:

> << >   Nevertheless, can you name me a fully erect, fully
>  four-chambered-hearted,
>   > ectothermic animal? >>
>   > 
>   > Any adult sauropod will do, I'd say.
>   
>   While you may be correct about the four-chambered heart(I suspect you 
>   are for several reasons), AFAIK no one really knows if dinosaurs had 
>   four chambered hearts.  >>
>  
>  Four-chambered hearts are >necessary< for any tetrapod to have long legs
and
>  an erect gait, because it separates the pulmonary circulation from the
>  systemic circulation. 

Perhaps, but one might as well theorize that endothermy is also necessary for
erect, long-legged tetrapods, as there are no erect, long-legged tetrapods
that we *know* to have been ectothermic, while there are thousands of species
of erect, long-limbed endotherms wandering around!


>  Elevated systemic blood pressure allows the evolution of "verticality."
All
>  known terrestrial vertebrates, large and small, with three-chambered
hearts
>  or incompletely four-chambered hearts are sprawlers or slitherers, simply
>  because they cannot muster the blood pressure required to bring blood back

> to the heart from erect limbs. 

They are all also ectotherms, which do not need the added speed and agility
of erect limbs!

>  For me, the
>  quadricameral-heart/erect stance argument is a clincher.

And for me, the quadricameral-heart/fully-erect-stance/endothermy argument is
just as much a clincher.


>  << > Indications are that adult fully endothermic sauropods would have
>  overheated,

As pointed out just recently on the list (and numerous times by Greg Paul),
large animals also take longer to heat up!  If your cold-blooded sauropod
ever got cooled off (by wind, rain, a dip in the lake) it would take forever
to heat back up.

>  By the way, a few sauropods seem to have evolved structures for
controlling
>  excess heat anyway: the sails of _Amargasaurus_ and the tall dorsal 
> vertebrae
>  of _Rebbachisaurus garasbae_.

Maybe.  Or maybe they were just display structures.  Or maybe they just
didn't hurt.


>   <<Any animal that had an 
>   endothemic metabolism would probably be stuck with it.  

>  hibernating mammals (for example) do turn down their
>  endothermy and are not endothermic all the time. 

Don't at least some bats and hummingbirds do this every night?  Of course,
bats and hummingbirds are hardly analogous to giant sauropods, although it
does show that such changes are possible.  Perhaps, however, this also shows
that it is only the smallest endotherms that require such drastic
energy-saving mechanisms.

>  Growth rates of juvenile dinosaurs of many kinds,
>  as observed from their bone growth patterns, were fast, but they slowed
down
>  with the onset of adulthood and maturity to the more typical reptilian
>  slow-but-perpetual growth pattern. This suggests a concomitant gradual
>  slowdown in their metabolism

So adult kangaroos and elephants are mass homeotherms too?

NP