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

[archosaur@usa.net]

Cool, the terramegathermy opus :)

Well seeing how much work went into this, I wanted to make sure and allocate
enough free time to responses.

Unfortunately that didn't seem to work; so I'll just see how much I can
respond to in the time I've got.

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> 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.

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

_____________________________


> Long:

> (Even though I quote large chunks, this is by far no substitute for  > the
actual article, especially its figures. *bold* _underlined_ in   > the
original)

++++++++++++++++++++++++++

True enough; I'll make a point of asking for extra info before going all out
on anything here, just to be sure.

__________________________

> "Among dinosaurs, megadinosaurs (those over one tonne) have been     >
considered among the best candidates for having had low metabolic    > rates
(LoMRs). Spotila et al (1991) argued that big dinosaurs were   > gigantotherms
that shared thermal characteristics with the large     > leatherback turtle,
and Dodson (1991) suggested that giant dinosaurs > lived in the slow lane
compared to giant mammals. Coulson (1979),    > Bennett (1991) and Ruben
(1991) restored big dinosaurs as "good      > reptiles" powered by bursts of
reptilian hyperanaerobiosis rather    > than the sustained tachyaerobiosis
that powers birds and mammals.    > [HP] Farlow (1990) suggested that large
dinosaurs were "damned
> good reptiles" with fluctuating metabolic rates (MRs), and in 1993 he >
argued that dinosaurs used a combination of rapid reproduction and   >
intermediate metabolic rates (InMRs) to grow bigger than land        >
mammals. All the above workers, and McNab (1983) and Dunham et al.   > (1989),
have modeled big dinosaurs as LoMR or InMR inertial          > homeotherms
that maintained constant body temperatures on a daily    > basis.

> *Why land giants must be tachyaerobic. -* [...]
> On land all classic reptiles with LoMRs have weighed about one tonne > or
less [...]. Many HiMR land mammals have exceeded one tonne, and   > the
largest approached 20 tonnes [a very high estimate for           >
*Indricotherium*, IMHO] [...]. This differs from the marine realm,   > where
6-15 tonne basking and whale sharks have LoMRs [...] [and are  >
poikilothermic and more sluggish than whales]. Therefore, when we are > asked
(again and again) why some dinosaurs were four to five times   > bigger than
land mammals, we ask why dinosaurs grew a hundred times  > larger than land
reptiles! [Severe doubts whether the biggest        > sauropods really reached
100 tonnes, or even half that,              > notwithstanding.]

+++++++++++++++++++++++++++++++++

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

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> Our hypothesis centers around the logical argument that living in the
> high energy field produced by gravity is a hard and constant struggle > that
can only be won with the great strength and sustained power     > inherent to
a high energy 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?

________________________



> *Leatherbacks versus elephants as dinosaur analogs. -* [...]         >
Leatherbacks [...] Heat generated by internally placed muscles during >
constant swimming and trapped by heavy fat insulation helps maintain >
moderate body core temperatures of ~30°C. Leatherbacks never         >
experience severe heat or tissue freezing temperatures."

> Thus, leatherbacks are indeed endothermic (HP "Jura" was right),
> bradymetabolic, bradyaerobic, and for practical purposes             >
homeothermic. 

AFAIK this combination is known as gigantothermy.

++++++++++++++++++++++++++++++++++

Yeah, that's kind of confusing since leatherbacks seemed to have been the
archetypes for what a gigantotherm is.

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> "Elephants of the desert Skeleton Coast of southwest Africa          >
[Namibia?] have long striding limbs powered by large volumes of      >
tachyaerobic muscles, high blood pressures, and high capacity        >
respiratory tracts. These land giants do not cruise constantly, the  > leg
muscles are placed away from the body core, and insulatory fat is > absent
(Haynes, 1991). Body core heat is generated largely by hard   > working
internal organs. The Skeleton Coast elephants not only       > survive in a
desert with limited resources by [...] [migrating]      > (Bartlett &
Bartlett, 1992), they are unusually gigantic with world  > record weights up
to 10 tonnes. [I'm not going to buy 10 tonnes. 7   > tonnes is already
considered extremely heavy for an African elephant, > and I've never read
more.] Rather than going belly up when it gets   > hot, they use high body
temperatures of 37°C and bulk to             > thermoregulate in extreme
heat.

> Proboscideans have experienced frostbiting temperatures (Haynes,     >
1991). [I think this refers to elephants easily surviving in European > zoos
and not to mammoths!]

> The form and habitat of leatherbacks could hardly be more different  > from
the dinosaur world. Acceptance of their use as primary models   > for
dinosaurs is therefore surprising - imagine the reaction if      > whales were
used as the primary analogs for dinosaurs! The structure > and hot climates of
elephants are very reminiscent of the dinosaur   > condition, and it is
surprising how many reject their biology when   > restoring dinosaur
thermodynamics.

++++++++++++++++++++++++++++

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)?

__________________________


> [...]

> *Muscles, blood pressures and breathing. -* [...] 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.

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).

More on this after I get the ref.
_____________________________________

> A croc or gator can outsprint a person, but loses speed after a few >
seconds (Grenard, 1991).
> Also, large reptiles are at high risk of death after long periods of >
intense exercise because large animals cannot quickly recover from   > the
toxic effects of anaerobiosis (Bennett et al., 1985)."

+++++++++++++++++++++++++++++++++++++

Again, there is a ref on crocodiles removing high lactic acid content after
intense excercise (to the point of exhaustion) and it didn't take very long at
all. Right now I know it is in the Journal of Experimental Biology, but I
don't have the exact ref. I'll get it tomorrow.

____________________________________

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

++++++++++++++++++++++++++

So archaeopterigiformes are considered large animals?

__________________________


> "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? _Testudo atlas_ was gigantic, but no sauropod.
_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. We also had a fairly large array of
rauisuchians and other reptiles. Are we sure that P&L are considering extinct
as well as extant reptiles?

_____________________________



> [...] 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.

_________________________


> There is another reason why giants need high blood pressures. Pumping
> blood up against the gravity well to the brain requires work. The    > 
higher the blood is pumped the harder the work must be - and        >
following the adage that one cannot get something for nothing, we    > presume
this is true even if special cardiovascular adaptations are  > present. 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. 

++++++++++++++++++++++++++++++++++

Demonstratably 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.

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> The high pressure hearts of most mammals, from mice to humans,       >
elephants, and whales, make up about 0.6% of body mass (Fig. 4, Table > 1).
Long necked giraffes have oversized hearts that produce unusually > high
pressures (Table 1)."

> "*FIGURE 4 -* Same scale figures of a 30 [hm, what about 15?] tonne
> _Brachiosaurus_ and a 30 tonne female sperm whale. The dinosaur is   >
restored with an 11 m long trachea, lungs [including attachment sites > for
air sacs] and a super high pressure 1 tonne heart. The whale's 7 > m long
anterior airway [the blow hole is at the rostrodorsal end of  > the head, and
the head is _huge_...], small lungs and normal high    >  pressure 150 kg
heart are shown."

> "*TABLE 1*

> *Heart size and heat production in a 30 tonne _Brachiosaurus_*       >
[insert, say, *Seismosaurus* if *B.* was lighter*]

> Resting MR in kcal/hour if it is.....
> mammalian............................*4000-8000*
> reptilian.....................................500-900

> total heart tissue mass cardiac heat
> as % of total body mass in kg production kcal/hour

> 0.6% single normal 180 1000
> (BP 100-130 mmHg)

> 1.3% single giraffe oversized 400 [lacking in the original]
> (BP 200 mmHg)

> 2.0% multiple cervical 700 *~2000*
> (BP 200 mmHg)

> 3.3% single super oversized 1000 *~3000*
> (BP 750 mmHg)"

> "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 that    >
require that the cell consume large amounts of oxygen in order to    > resist
osmotic flow and maintain a proper chemical balance with      > surrounding
tissues (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

+++++++++++++++++++++++++++++

Hmm, there appears to have been more here (no doubt in pt 2) so I'll head to
that, I guess. 

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

Just a thought.

Jura

Jurassosaurus's Reptipage: A page devoted to the study of and education on,
the reptilia:

http://reptilis.net

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