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Re: [Re: [Re: ... vs energy efficient gigantothermy (boo hiss)]]

"David Marjanovic" <david.marjanovic@gmx.at> wrote:
> > I have no problem agreeing with that, but it does leave me with a bit > >
of a quandary; why is the lack of multitonne birds attributed to     > >
environmental factors (e.g. no big game, died before their time)     > > while
the lack of multitonne reptiles (excluding dinosaurs) is       > > attributed
to their physiology.
> > Did one ever stop to think that the reason why _M.prisca_ never got   > >
any bigger was because it was large enough to be an effective        > >
predator of moas.
> No moas in Australia, never.


Oops, I meant the Australian elephant birds of the time, like _Genyornis_.


> Well, this may be true for *Megalania*, there is only negative evidence > in
this case. However, why didn't diadectomorphs or pareiasaurs (or,   > for that
matter, dicynodontids etc.) reach sizes over 1 t or so?


It is a good question; especially considering that therapsids went from
relative giants (dinocephalians) to increasingly smaller and smaller animals
as they became more endothermic (i.e. more evidence for mammalian lifestyle
appears in these smaller more derived therapsids). 

All I can think of is that these animals were large enough to handle their
prey; though this doesn't explain why no Permian herbivores hit the gigantic
sizes that Jurassic sauropods did.

Maybe all the Jurassic flora was on Miracle Grow? :)


> > > > Yes, and these mammals also have anatomical "cheats" that allow them>
to hold up their large bodies with very little muscle use (e.g. the
> > > > locking mechanisms of elephant and ungulate legs). A reptile with
> > > > equivalent "cheats" wouldn't find it so hard to hold itself up
> > >
> > > This works only in _standing_. Not in walking.
> >
> > True, but free oneself from the aerobic problem of lung compression  > >
while walking and, possibly, lower the cost of locomotion and there   > >
should be no problem.
> Locking mechanisms, AFAIK, only reduce the cost of standing, not that of
> locomotion and lung compression during locomotion.


Yeah, I wasn't referring to the locking mechanisms in particular. I only
assumed that sauropods had freed themselves from this sinsoidal movement, or
found ways around it (possibly using their air sacs). 

> > Incidentally, since we are talking about sauropods, would it not make
> > more sense to have these "cheats" in place if one isn't going to be
> walking
> > half as much as they will be standing?
> Sure. Just that these are AFAIK no use for walking, and they did walk,
> however much or little.


True, but I question the need for a tachymetabolism to walk a couple of meters
at a time.


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