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... vs energy deficient gigantothermy (boo hiss)



To speed up the traffic today... :-)

----- Original Message -----
From: <archosaur@usa.net>
To: <GSP1954@aol.com>
Cc: <dinosaur@usc.edu>
Sent: Friday, May 04, 2001 9:31 AM
Subject: 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.

And birds are K-strategists, and they have IMHO not yet had a chance to grow
to gigantic sizes. The carnivorous ones had no gigantic prey available, and
the herbivorous ones are seemingly too young (the biggest aepyornithids and
moas were among the last).

Of course, this changes if we interpret "birds" as Aves, accept the usual
definition of Aves as *Archaeopteryx* + Neornithes, and "accept" my
phylogeny... then the biggest bird weighed something between 4 and 7 tonnes,
was 12 -- 14 m long, and is known as *T. rex*. B-P

> *snip*
>
> 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).

No idea about varanid MRs. :-(

> > 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).

I have yet to read this... how can all aquatic animals be obligate
homeotherms when water temperature changes?!?

> [...] (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?).

Mammals are K-strategists. If all adults and subadults die, the population
can't recover ever again in all species I can think of right now. See my
second post on the original P&L paper.

> 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.

What is vasomotor control?

> 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

OOC -- you trust a paper from 1942 that is apparently based on observation
in a zoo? This is so old that I didn't even know that The Beast was ever
called "Drachenwaran" (the e must be a typo) in German!

> 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.

Well, I have to find this... some time...

> 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.

yep

> > , 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?

Relatively short _distances_, IMHO, relative to one another.

> 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.

This works only in _standing_. Not in walking.

> 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 neck was quite inflexible. Sauropods could browse within a large _area_
while standing, but not within a large _volume_.

> > 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.

Giant tortoises move very slowly (little costs), and how high above the
heart do they carry their heads? 1/2 m? 1 m?

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

Hm. Diplodocids had necks that faced forward (not down), and euhelopodids
and brachiosaurids had necks that did face up. And imagine a diplodocid
standing tripodally...

> > 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.

Turtles are quite immune to predation, aren't they?

:-)