Re: [Terramegathermy in the Time of the Titans (long...)]

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

> > Very short: Standing is exercise and requires muscle work, the larger >
the
> > animal, the more. Leatherbacks are gigantothermic, but ridiculous >
analogs
> > for dinosaurs, desert elephants are better.
>
> I disagree; it all depends on the context. I wouldn't use leatherbacks as
> examples of how a bradymetabolic animal can stand, since leatherbacks
can't,
> but they are good examples of alternative ways of achieving endothermy
without
> resorting to tachymetabolism.

Sorry, I shortened this too much, look at the "long" part :-]
__________________________________

> > Anaerobic production of power is impossible for vertebrates to > sustain
for
> > any reasonable time -- it is an emergency solution       > _only_. Big
animals
> > require big, tachyaerobic muscles require big
> > hearts require more energy than a bradymetabolic animal can produce, >
and
> > that 24/7.
>
> Out of curiosity, what examples did P&L use for this scenario?

All I can find is table 1... look at the "long" part :-]

> Did they take
> into account anatomical adaptations that allow for long periods of time
> standing without much muscular effort?

Surely not. Horses have such adaptations, but do elephants have any? Or any
dinosaurs?

> It should probably be stated that this is in regards to *extant* reptiles
> which are all significantly *smaller* than their prehistoric relatives.

That is in regard to *Megalania*, which P&L think weighed about a ton and
was the limit for terrestrial LoMR animals, and *Geochelone atlas*
(obviously synonymic with *Testudo atlas*), which is considered to be in the
same weight range. *Megalania* is shown in Fig. 1 as a silhouette with a
small ilium and as long as a mammoth. (This silhouette has a rather short
tail, I'd say.)

> > [...] gravity [...] sustained power [...] tachyaerobic system. The
belief that low
> > energy bradyaerobic
> > forms can bear the burden of great bulk is naive. > Being an aquatic
giant is
> > much easier because water is a low energy  > environment where buoyancy
> > negates the effects of gravity, and       > swimming is five to twelve
times
> > more efficient than walking the same > distance.
>
> Y'know I'd often wondered about that statement. If one has to work twice
as
> hard to get half as far in water (due to the high friction), why is it
more
> efficient? Does the low gravity really make that much of a difference on
> energy use in locomotion?

Every slight movement in water moves the whole body. Not so on land.
Additionally, on land the weight must be supported during movement by extra
muscle work. So, while usually not true for one and the same species,
everything as hydrodynamic as a sea turtle needs very little energy for
sustained movement.

This is why P&L consider all aquatic and semiaquatic animals as irrelevant
for hypotheses on dinosaur metabolism.

> Again, because leatherbacks achieved endothermy without tachymetabolism.
But
> if we prefer to stick with more terrestrial types, why not use Komodo
dragons
> (much more on this later)?

Because varanids never reached more than 1 tonne or so, I think.

> > The skeletal muscles of birds and mammals are about twice as large as
those of
> > reptiles at a given body size (Ruben, 1991). [...] [Dinosaurs
> > including birds and mammals have longer ilia = larger leg muscles than
> > reptiles of the same mass, Fig. 3..] Why do reptiles have such small leg
> > muscles, and birds and mammals such large ones?
>
> Well, for one, a lot of that muscle size is devoted to generating body
heat,
> hence why a reptile of the same strength as a similar mammal would look
> smaller.

Oh, the muscles are not there to generate body heat alone. They all do
mechanical work. A lot of heat is AFAIK generated by the liver.

> Another reason...
>
> > is that reptile muscles can produce twice as much anaerobic power as
those
> > of mammals and birds (Ruben, 1991), so even small legged lizards and
> > crocodilians sprint at high speeds. However, hyperanaerobiosis
> > is an inefficient process (that consumes ten times as much food as
> > aerobiosis) that works only for a few minutes, and is followed by toxic
> > effects (Bennett, 1991). For example, anaerobic power falls off so
> > quickly that big crocs may be unable to drag smaller ungulates into
> > deep water to drown them if they do not succeed with the first lunge
> > (Deeble & Stone, 1993; contrary to the assertion of Bennett et al.
(1985)
> > that big reptiles can produce hyperanaerobic power for long periods).
>
> Interesting proposal, but quite different from what I've read. Crocs have
a
> phenomenal degree of anaerobic endurance. They can withstand a lactic acid
> content of near 80%, which is higher than any known animal, and it doesn't
> take them that long to get rid of it either (I believe it is about 3 hours
or
> so, but I'll have to get the ref to be sure).

Not that long??? 3 hours???

This is why I wrote

> > This spells DOOM to any ideas about bradymetabolic *Archaeopteryx*,
> > enantiornitheans, ... (Insert Chopin, "Marche funèbre".) B-)

And - can you imagine a sauropod walking for some minutes, then dropping to
the ground and resting for 3 hours?

> More on this after I get the ref.

I'm looking forward, but I doubt it will actually contradict the above!

> So archaeopterigiformes are considered large animals?

No. But they couldn't have to rest an hour after a minute (or was it 10
seconds in the calculation?) of flight.

> > "The lower anaerobic power production of tachyaerobic muscles means  >
that
> > birds and mammals need larger leg muscles than reptiles to      >
produce as
> > much overall burst power. [Archie has long ilia, _ô surprise_.] The
> > inability to carry massive bulk with small anaerobic > muscles helps
explain
> > why really gigantic reptiles have always been  > aquatic.
>
> What constitutes gigantic?

In this paper, everything heavier than 1 tonne. This makes *Megalania* and
*G.*/*T. atlas* just marginally gigantic.

> _Purussaurus_ was a giant alligatoroid that might have been terrestrial
(only
> the skull is known, but the strange bony trench running down the snout
would
> seem to discount a semi-aquatic lifestyle.

Never read of this one... How big was it?

> We also had a fairly large array of
> rauisuchians and other reptiles.

A fairly large array of fairly large, but not gigantic reptiles :-) , none
AFAIK larger than *Megalania*.

> > [...] The low capacity and low pressure respiro-circulatory system of
> > reptiles can deliver only enough oxygen to supply bradyaerobic
> > muscles. [...] [Large, tachyaerobic muscles require good, large lungs
and
> > hearts as well as high blood pressures.]
>
> So what reptiles were being studied with this? Varanids are highly aerobic
> reptiles, complete with gular pumps and alveolar lungs. They might not be
> called tachyaerobic, but I wouldn't call them bradyaerobic either.

OK, varanids are "very good reptiles", but how much difference is there
between varanids and other reptiles, and varanids and mammals? (Leaving out
birds here for unfair competition. =8-) )

> It is not possible to pump blood more than 0.5 m above heart level with
low,
> reptilian circulatory pressures and brachycardiac work (Seymour, 1976),
> so no land reptile has a long erect neck.
>
> Demonstra[...]bly false. _Geochelone nigra_, the Galapagos tortoise
(saddle back
> variety) has an extremely long neck that is often held high above the body
in
> a very sauropodian "S" shape. And they accomplish this with a three
chambered
> heart.

How high above the body?

> > "A consequence of high aerobic capacity and high circulatory pressure is
> > high resting MRs. In order to process large volumes of oxygen when
> > exercising, tachyaerobic muscle cells have 'leaky' membranes [...]
> > (Else & Hulbert, 1987). Failure to properly oxygenate the
> > tissues of tachyaerobic animals results in a shutdown of the system
causing
> > torpor, so failure to maintain high blood pressure even when resting
> > results in torpor.

> > [...] [All organs must work hard in tachyaerobes to supply one
> > another.] The high oxygen consumption of tachyaerobic cells and the hard
> > working internal organs adds up to a resting metabolic rate that is
nearly
> > as high as the entire oxygen consumption of active [!!!] reptiles with
low
> > pressure circulatory systems (Jansky, 1965, who notes that cardiac work
> > is an increasingly large part of the resting metabolism in larger
mammals[*]).
> > This is why vertebrates always have low exercise/resting aerobic ratios.
> > Long anterior airways pose a respiratory problem because they hinder
> > ventilation

*This is why P&L even say that the resting metabolisms of sauropods must
have risen rather than decreased with age & size, in contrast to hypotheses
of gigantothermy, mesothermy and the like.

> I will say this though; so far the calculations done above are for
supplying
> blood [to?] tachyaerobic muscles, what about bradyaerobic muscles?

I don't know. The actual calculations are not published, at least not in
this paper (his refs to Paul, 1991 and Paul, 1994 might contain them).
However, bradyaerobic muscles are simply not enough for an animal of
sauropod size to walk around.

> Just a thought.

Same!