Terramegathermy in the Time of the Titans (long...)

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

Considering that HP Gregory S. Paul seems not to have the time to explain
his ideas himself, while they are relevant to some current threads, I'll try
to summarize his & Guy D. Leahy's paper "Terramegathermy in the Time of the
Titans" which was published in the 1994 Dinofest volume. (This is difficult
without retyping the whole paper, however, because there's so much
information in it...)

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. 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.

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)

"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.]

    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.

[...]

*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.

"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.

[...]

*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? One 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). 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)."

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

"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.
    [...] 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.]

    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. 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