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Re: energy wasteful terramegathermy (hooray) vs energy efficient gigantothermy (boo hiss)]



> It is interesting that after 300 million years of evolution classic,
> bradymetabolic, bradyaerobic land reptiles have never become truly     >
gigantic either in height or mass. But dinosaurs became very tall and   >
reached many tonne status soon after they appeared, and mammals also   >
evolved real giants fairly quickly after giant dinosaurs went extinct. > Ever
wonder why? This disparity has not really received that much      > attention,
probably because the view that terrestrial bradyaerobes can > become gigantic
remains popular in some circles. But can they? 

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

Truly an interesting question, but before one decides to pin this gigantism on
endothermy, let's also remember that 140 million years of evolution has yet to
produce a bird that even comes in at a tonne, much less a multitonne one; and
birds are twice as metabolically active as mammals.

____________________________

*snip*

> Besides, even if leatherbacks had elevated MRs this would not           >
necessarily have meant that all big reptiles converge with big mammals, > it
have instead might have meant that leatherback MRs were elevated    > above
those of other reptiles. Giant tortoise and croc MRs show no     > evidence of
being above the predicted reptile line.

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

And what about varanid MRs; in fact I rarely saw varanids even get a mention
throughout this paper (though I was relying on what HP Dave Marjanovic was
posting).

___________________________

> Deep core body temperature measurements of multi-tonne basking sharks  >
show that they are poikilothermic and therefore almost certainly       >
bradymetabolic, with MRs probably one tenth the whale level (probably  > true
of whale sharks also).

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

How can basking sharks be poikilothermic if all aquatic animals are obligate
homeotherms (see Cowles's comment in Science vol 105 pg 282 for more on this).
No argument over the bradymetaboly.

___________________________

> There is no evidence that the 10 fold difference in MRs
> does not apply to giants as well as teeny weenie vertebrates. Of course >
giant, tachymetabolic, tachyaerobic rorquals are far more active and   >
energetic than filter feeding sharks (scuba divers can easily keep up  > with
the latter, not the former), confirming that large size does not  > force a
major convergence.

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

Well since basking sharks come in as medium humpback whales at best (and are
completely outclassed in size by the other two rorquals) I'm not too surprised
that have an easier time keeping up with them than the larger animals, who can
push more water out of their way than smaller ones (though to my knowledge no
one has gone diving with either of these two species so I don't know how it
pans out). Alright though; for the sake of argument lets say that basking
sharks are equal in size to humpback whales. Basking sharks are planktivores,
humpbacks are not.  Fish form a large portion of a humpback's diet and as
such, a speedier means of pursuit is in order to catch them. Conversely
plankton are pathetically easy to catch if you have the right equipment, and a
speedy aproach is hardly called for, unless trying to escape (which doesn't
work too well for these fish since they are not designed for any real speed).


A much better comparison would be with whale sharks, which do regularly reach
rorqual weights and, incidentally, are a pain to keep up with underwater.

_________________________________



> At this time, it is not certain what the hypothesis of gigantothermy is >
based upon, or even what it actually means. Nor does it explain why    >
bradymetabolic/aerobic reptiles have failed to evolve into land giants > for
so long. 

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

Unless, of course, dinosaurs do represent these bradymetabolic/aerobic
reptiles. Since no animal in the history of the planet, has ever gotten as
large as the animals that came out of the Mesozoic, it makes for a highly
debateable proposition (e.g. if mammalian metabolism is really required to
reach sauropod sizes then how come the largest mammals we know of, barely hit
mid sauropod size throughout their "dominance" of the planet?).

________________________________

> (Despite being bradymetabolic leatherbacks are homeothermic endotherms, >
because they use the constant activity of swimming and countercurrent  > heat
exchangers to maintain an elevated level of body heat and         >
temperature. The same is true of some tuna and sharks. These options   > are
not available to land animals which are not constantly active, and > cannot
thermally isolate their thermally exposed leg muscles with      >
countercurrent heat exchangers). 

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

What, vasomotor control is suddenly not an option? This physiological
mechanism is one of the main things that keeps many large varanids
(_V.giganteus_, _V.varius_) warmer than their environment. According to HP
Dave Marjanovic, countercurrent heat exchangers are also present in large
wading birds (storks and other spindly legged animals), though it admittedly
seems to do the opposite thing for them

_________________________________________

> On land mammals have reached 20 tonnes, classic reptiles only a tonne   > or
two (there is no way that the biggest tortoises weighed 4 tonnes    > which is
as big as African elephants, it is not yet certain whether the > super moniter
Megalania was fully terrestrial).

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

And land birds 1/2 a tonne; you know, for perspective.

_____________________________________



> This is opposite the common but illogical assertion that sauropods grew > so
big because they had low MRs. Terramegathermy is based on the       > logical
and rather obvious premise that since land animals live in 1 G, > tall and/or
massive giants need to have high energy power systems in   > order to cope
with living under the pull of an entire planet. The       > extremely low
aerobic exercise capacity of all bradyaerobic animals of > all sizes, and
regardless of limb design and posture, limits them to   > sustained walking
speeds under 2 km/h (claims in the literature that   > oras regularly move at
5 km/h are not substantiated by data sets [when > I asked one researcher for
his data he said it was lost] and are       > spurious, oras plod along at
1-2km/h like other big lizards)

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

From: Ecology of the Komodo Monitor

"Normal walking and searching is carried on at a speed of approximately 4.8
km/hr (our observations agree with those of Lederer, 1942)."

Work Auffenberg cited:

Lederer, G. 1942. Der Drachenwaren (_Varanus Komodoensis_ Ouwens). Zool. Gart.
(Leipzig), (n.s.) 14 (5/6):227-244

So there's two independent ora studies showing that these guys were well above
1-2km/hr and I find it very hard to believe that Auffenberg would mess up the
numbers on this one, since he did do the *most comprehensive* study on oras to
date. 

I noticed his ref wasn't in your list. In fact, I'm not sure what, if any,
reference given had anything to do with Komodo dragons.

Again I admit that I don't have the paper handy and am relying on Dave's
posting. The one, in particular, that I'm basing this off of can be found
here:

http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00379.html

In which he, I assume, gives all references listed.

_______________________________________


> , so they cannot migrate long distances regardless of size and limb    >
form and none do so (crabs, snakes etc migrating relatively short       >
distances do not count).

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

Define relative; are we talking relative to a 6ft tall human or a 5ft long
snake?

__________________________________

> It cannot be overemphasized that body temperature stability does       >
absolutely nothing at all in any way or regard to solve this problem   > for
reptiles, because a reptile with a body temperature of 98F 24 hrs a > day
every day of the year will still have the same pathetic aerobic    > exercise
capacity it would if its temperature drops 20 degrees at      > night. 

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

Demonstratively false, and in fact, quite the opposite at times. See:

Autumn, K., Farley, C. Emshwiller, M. and Full, R.J. 1997. Low cost of
locomotion in the banded gecko: a test of the nocturnal hypothesis. Physiol.
Zool. 70, 660-669

And another ref on low cost of locomotion as soon as I can find it.

Both basically state the observed instance of *increased* aerobic locomotory
ability in nocturnal geckos even though, they are at a thermally suboptimal
level when doing it.
_________________________________


> Because according the refs cited in my papers long migration (1000s km) > is
extremely energy taxing and physically arduous, only tachyaerobic   > mammals
move far on land. Claims in the literature that bradyaerobes   > can actually
migrate farther than tachyaerobes while walking at speeds > of 3-4km/h are
false in that bradyaerobes simply cannot sustain such   > high speeds, and are
improbably speculative in face of the inability of > land bradyaerobes to
migrate long distances. Bradyaerobic land giants  > would therefore at best be
slow, and unable to move very far. That's if > they would work at all. Because
bradymetabolic animals inherently have > low capacity central organ dependent
respiro-circulatory systems, they > cannot oxygenate and feed large, high
aerobic capacity sets of muscles, > so they are inevitably bradyaerobic (ergo,
all reptiles have relatively > small leg muscles, anchored upon very short
ilia in the thigh). It is  > questionable whether such small, low capacity
muscles can adequately
> support a giant body in 1 G, at least without frequent belly resting   >
which would be a tad awkward for something weighing 50 tonnes or so. We > KNOW
that the large, high aerobic capacity of bradyaerobic mammals can > carry huge
bodies around all day long and more (and their large limb   > muscles are
anchored upon long pelves at the thigh).

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

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 either. 

The only thing that stops oras (which are very aerobic) from migrating long
distances, it seems, is their limited distribution. I'll see if I can find a
paper on _Conolophus_ nesting migrations, since going from the Galapagos
lowlands, up a mountain and down into a caldera and then back again is no mean
feat.

On a side note, we are talking about sauropods (mostly) here. How far and how
fast do you think an animal has to move when it has a neck stretching out
20-40 ft ahead of it?

____________________________________


> (The Bennett et al. study on anaerobiosis induced fatique in big crocs >
does not offer definitive evidence of the ability of big reptiles to   > use
anaerobiosis for sustained activity. For one thing they did not    > actually
measure the amount of work being done by the struggling crocs. > A big croc
doing anything in close quarters might seem periodically    > "explosive", yet
may be only achieving modest levels of exercise. In   > any case we have no
idea how much walking speed the effort would       > translate into because
there were no power measurements. 

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

1) I wasn't using this study as evidence of dinosaurs moving anaerobically
(especially not hyperanaerobically which is just ridiculous), I used it to
show that, contrary to popular belief, crocodiles do have a rather high
endurance. It's just that their endurance is all anaerobic (which, of course,
makes sense when most of the work is done underwater).

2) As HP Adam Britton has already said on list (hopefully he doesn't mind me
giving a quick quote):

http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00431.html

"...However, it's not so simple. Crocodilians exert massive amounts of power
over short periods of time (a large croc [>5 m] can separate the front half of
an average sized ungulate from its posterior portion with a flick of its
head), "

So I really doubt that Bennet et al's studies showed crocs doing "moderate
excercise."

__________________________________


> More informative is the case of spindly legged gnu, which after being   >
snatched at a waterhole by a croc twice its size was able to
> brace itself and resist being pulled into the water for 20 minutes     >
[until other crocs came along] because the massive reptile so quickly  >
exhausted itself that it was not able to overcome the superior         >
sustainable aerobic capacity of its smaller mammalian prey.

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

Did this come from:

DEEBLE, M. AND V. STONE. 1993. Giant crocodiles - deadly ambush in the
Serengeti. Natl. Geog. 183(4):94-109.

If not, I'd love to hear the ref on that one, since it very much sounds like
an odd exception. I've seen the power that crocs exert on their prey (NG's
Last Feast of the Crocodiles showed an average sized Nile croc grab a large
ungulate by the head and literally throw it over its body into the water) so I
find it hard to believe such a stalemate would arise. 

____________________________________


> Besides, big crocs often die after doing heavy anaerobic work. 

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

And your bases for that is?

All but one of the crocs in Bennet's study showed substantial (if not full)
recovery of hyperanaerobiosis within 3-4 hours after activity. The *one*
acception was the croc that went so nuts that it wound up lowering its blood
PH to 6.42 and was out for 29 hrs. Most crocs *don't* do this (usually because
prey don't survive long enough) and the majority of croc deaths that are
reported (from this type of exhaustion) come from failed croc captures that
were relying on the animal to exhaust itself. As such, they hardly make for
worthy statistics.

___________________________________

> Finally, animals just do not regularly use anaerobiosis to regularly do >
sustained work such as walking for half an hour or more each day, its   > too
toxic and will damage the creature in the long term. Modeling      > dinosaurs
as using anaerobiosis for regular movements is not going to  > get very far,
as it were.)

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

Agreed.

________________________________

> It is questionable for inherent circulatory reasons that others have
> discussed whether a high pressure, truly four chamber heart is         >
compatible with bradymetabolism. Conversely, bradymetabolic organs     >
probably cannot support a heart powerful enough to produce high        >
pressures. Because reptiles have only low pressure hearts, they are all > low
slung even when large.

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

I wouldn't call giant tortoises low slung at all, and they have three
chambered hearts.

Kinda interesting how all the longest sauropods had necks that aimed down and
not up.

______________________________


> Tachymetabolic bird and mammal hearts can produce the very high        >
pressures needed to carry the head well above heart level, resulting in >
giraffes. Because tachymetabolic animals have stable body temperatures > even
when small they than can gather food for a larger portion of the  > day than
can reptiles. Because tachyaerobic metabolic systems allow    > them to
sustain high walking speeds and extended bouts of high activity > without
profound fatique, they can gather much more food per unit time. > This allows
tachymetabolic/aerobic mammals and birds to grow far faster > than continental
reptiles (although some marsupials and primates grow  > no faster than the
fastest growing reptiles) under natural conditions  > (spare me the notion
that since farm raised crocs kept constantly warm > all day long and/or feed
vast quantities of food at no expense to      > themselves suggests that
reptilian dinosaurs could magically have grown > as fast, since no one was
raising dinosaurs on Mesozoic farms where    > they could be kept constantly
warm all day long and/or feed vast        > quantities of food at no expense
to themselves). 

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

I will "spare" you the farm raised croc example when you can show that no such
environment is available to wild animals. If you look back through this
thread, namely these two posts:

http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00431.html

http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00450.html

you can see that such "ideal" conditions can and do exist in the wild. That we
have around 50 species of lizard (_Varanus_) that all opt for higher metabolic
lifestyles, would indicate that creatures can make a living off of these types
of conditions.

What I have not seen in your terramegathermy proposal so far (again, I admit
to not having read through the entire paper. A problem that will hopefully be
rectified soon) is the acknowledgement that bradymetabolic animals are highly
dependent on their environment when it comes to growth and these environment
dependent growth rates dramatically effect calculations. This is one big
reason why sexual maturity is usually decided by size rather than age with
bradymetabolics since the time it takes to reach said size can be markedly
different for each individual depending on the environment it lived in. This,
along with lack of study done on most reptiles, makes me question the validity
of lumping all reptiles in the "slow growth" basket.
___________________________


> Because it is not possible for continental animals exposed to numerous >
disease vectors and predators as well as accidents to live more than 60 >
years or so, all giant animals must grow rapidly. 

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

Though, in general, I agree with this statement, we do have continental
chelonians (_Terrapene_ for one) that regularly reach centennial years, and
giant tortoises (which were also probably centennial) were once common
continental animals as well. So there are a few exceptions there.

___________________________________________

> Dinosaurs - Some people, those who prefer to not carefully read my     >
papers, actually think that I'm one of these hardcore "hot-blooded"    >
dinosaur people that think all dinosaurs had the energetics of         >
hummingbirds on speed. Of course the more knowledgeable among you,     > those
who have truly read my papers are rolling on the floor with      > laughter at
the thought.

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

Well assuming that your attitude on dinosaur metabolics hasn't changed much
since Predatory Dinosaurs of the World, then my qualms are really only that
you state that reptiles can't do it with the metabolisms that they've got.
Since reptilian metabolism differs for each group, I don't think this is a
fair assessment.

As for sauropods with the metabolism of hummingbirds on speed; that's just
scary :)


Jura




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

http://reptilis.net

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