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

[archosaur@usa.net]

> 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?

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Um, I'm not sure if elephants do or not, though I do believe that they do.
Standing stiff legged with the legs directly underneath might use less
muscular effort. I'll have to look it up though.

Weren't there studies done on theropod legs, that showed them in a bent
position when at rest? Seems awfully tiring for muscles to hold up a
multitonne body for long periods of time if the animal's legs are always bent;
unless there were some nice energy saving tendons and ligaments to make the
job easier. 

Guess I'll put that one on the list of refs I'm dying to look up ;)

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> 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.)

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*Gotta find the frickin _Megalania_ paper*

I wish I knew how much of the skeleton of this animal that we've found. In
particular, limbs of the beast along with the hips they went into. I'll see
what I can find on this guy before I go too far into _Megalania_ size again.

As for the tail, while I don't have the figs handy, a short tail might have
been possible if it was proportional (or as a-proportional) as a Komodo
dragon, which also have short tails.

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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.

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Fair enough then.

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> 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.

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I thought they were arguing about large reptiles locomotion on land.
Admittedly the largest Komodo dragon only weighed 365 lbs, but that is still a
lot of weight to lift. Worth considering if they want to do _Megalania_
comparisons as well.

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> > 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???

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Let me put it this way; if I were, somehow, able to survive such a low blood
PH, it would take me a hell of a lot longer to remove all that excess lactic
acid than just 3 hrs. 

The first time I went rock climbing I blew out my pectoralis and intercostal
muscles. It took me 3 days before the aching had disappeared.

For the record though, I am not stating that sauropods were walking around
anaerobically like crocs, just that the oft stated notion that crocs have no
endurance is not quite true. They have good endurance, it's just all anaerobic
(which makes sense when the majority of one's fight time is underwater).

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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?

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Anything sauropod size should be able to withstand anaerobic exhaustion for
more than just a few minutes. Besides, how far does one need to walk when one
has a 12-30ft neck stretched way out ahead of them.

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> More on this after I get the ref.

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

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This might take a little longer than I thought. I couldn't remember what
article I had originally recieved the reference from (might have been Ruben's
_Scipionyx_ paper). 

On the bright side though, HP Adam Britton has given me a hand in the right
direction.


Bennett, AF, Seymour, RS, Bradford, DF and Webb, GJW (1986). Mass-dependence
of anaerobic metabolism and acid-base disturbance during activity in the
salt-water crocodile, _Crocodylus porosus_. J. exp. Biol. 118: 161-171

The paper that I am thinking of was just prior to this one and was in the same
issue. In fact the above was used as a follow up to it.

So I'll see if I can *finally* get it by tomorrow.

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> 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.

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But toxin removal in crocs is size dependent, as HP Adam Britton has already
mentioned. A tiny (sorta tiny) archaeopterygiforme would take significantly
less time to remove lactic acid content in its blood from high anaerobic
exertion.

Of course the best way to avoid this would be to become a aerobic animal.
Varanids did this and still retained their bradymetabolism, I don't see why
archaeopterygiformes couldn't either. Especially with the higher O2
concentration back then.

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

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Hmm, the largest tortoise hits 550 lbs. _Testudo atlas_ was the size of a VW
beatle. Estimates I've heard place it in at 4 1/2 tonnes.

Surely that makes it more than just "marginally gigantic?"

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> > _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?

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I'm not sure of the exact measurements, but you can see a neat picture of the
skull next to a person for comparisons.

http://reptilis.net/index4/purussaurus-skull.jpg

Unfortunately the picture doesn't show the ridge in the snout too well. I'll
see if I can upload a topdown picture if you'd prefer.

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> 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-) )

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And other reptiles? With that criteria it might be a little hard to decide how
different they are.

Varanids are the only reptiles with alveolar lungs, during sustained bouts of
aerobic activity they use gular pumping to completely fill up their lungs
while walking fast and while running they hold their bodies stiff and only
move their limbs, thus allowing for aerobic running as well.

Earl (1982) has shown that mean oxygen consumption for _V.bengalensis_ is
significantly higher than expected based off of other large lizard data, but
not beyond the range of other varanids. This higher O2 consumption makes
varanid body temps higher than expected. Varanid metabolisms are also much
higher than other lizards studied (mostly iguanians) but still under most
mammals & birds.

Bartholemew and Tucker (1964) discovered that varanids are capable of
increasing body temperature endogenously as well as using normal ecothermic
means.

Now gular pumping has been noted in other active lizards and it is the opinion
of Owerkowicz et al (Science, 1999) that this is actually primitive to all
lacertilians (basing it off of similarities to fish gular pumping). Endogenous
heat production is also seen in snakes as well.

Other than that though, this is much of what separates varanids from other
reptiles.

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How high above the body?

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It's pretty darn high (they do it while standing as well). I have a pic that I
can upload later. When I do, I'll post the link.

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> > 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.

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I don't know; I'd prefer to see how they calculated it and what reptiles it
was based off of first before stating one way or another (again, crocs of
similar size to large tortoises can't stay on their own four feet as long as
the chelonians).

More to come :)


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

http://reptilis.net

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