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Re: sauropods: homotherm,heterotherm or gigantotherm?



--- David Marjanovic <david.marjanovic@gmx.at> wrote:

> > Well, it WOULD gather food much more quickly. It
> would
> > have to, since it would use the food up much
> faster. I
> > don't know of any evidence to suggest any
> > physiological increase in food gathering ability,
> 
> Well, higher endurance should lead to the ability to
> walk around all day...
> 
> ...and then there's the metabolic work needed for
> just _standing_, which 
> possibly requires tachymetaboly above some threshold
> body size.

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

Depends on whether or not automatic endothermy
actually does result in an increase in aerobic
capacity (and not just an increase in aerobic
requirement). That is very much still up in the air.
Most creatures that have a large aerobic scope, are
ones that need a large aerobic scope (e.g. dogs and
horses). 

Speaking of horses, they and other critters have
joints that lock while standing, which conserves their
energy.

________________________________________


> > being coupled with a switch to automatic
> endothermy.
> 
> Is that how you call endothermy produced by
> tachymetaboly?

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

Yeah, Bakker coined the term back in the 1980, during
a symposium of the American Association for the
Advancement of Science. It was published in the book:
A Cold Look at the Warm Blooded Dinosaurs. 

Bakker got the end paper, entitled: "The Need for
Endothermic Archosaurs." 

In it (and later in Heresies) he mentions that the
type of tachymetabolic endothermy seen in extant birds
and mammals, varies markedly from the endothermy seen
in fish, insects, monitor lizards, leatherbacks and
skunk cabbage. 

Since it involves heat generated, mainly by the
viscera (instead of the muscles), and since it (for
the most part) cannot be turned off; it warrants the
term: automatic endothermy.  

It seems to be a good enough moniker for these talks.
Especially since those who are in favour of 
pro-endothermic dinosaurs, always seem to mean:
pro-tachymetabolic-mammalian/avian-type-endothermy.

_______________________________________________


> > I think there's a misconception prevalent here. A
> 10
> > degree change in temperature will change digestion
> > speed, NOT digestive efficiency. A reptile that is
> > digesting a meal at 10 degrees less than the
> optimum
> > temperature, will still digest that meal much more
> > effectively than most mammals (possibly most
> automatic
> > endotherms in general). It will just go slower.
> 
> OK, but this limits the _eating_ speed of
> poikilothermic animals, doesn't 
> it? (I mean that you can't eat faster than your
> digestion can keep up.) I 
> wouldn't recommend such a limit to a growing
> sauropod...

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

Why? Since when were sauropods living in zones
temperate enough for this to even become an issue?

_______________________________________________
 
> > If dinosaurs had digestive systems more in line
> with
> > other reptiles, than mammals (at least. I'm still
> not
> > sure about the birds), then we would expect them
> to
> > require less food than a similar sized mammal.
> Judging
> > by the relative efficiency suggested by the
> > _Tyrannosaurus_ coprolite, it would appear to be
> that
> > way.
> 
> What do you mean? That coprolite contains plenty of
> bone fragments that 
> don't occur in crocodile droppings.

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

True, but they do occur in ora droppings. Besides
that, the point is that this particular
_Tyrannosaurus_, didn't pick the meat off the bones
like most mammalian and avian predators do. To
paraphrase the old Alka Seltzer commercials: "it ate
the whole thing."

This suggests that theropods (tyrannosaurs, at least)
didn't leave much behind when they were done.

__________________________________________________

*snip*

> > We also had all the many
> > (seem to be coming out of the woodwork lately)
> > terrestrial crocodylomorphs that were, at least,
> on
> > par with the largest terrestrial cats today.
> 
> See above, and we don't seem to approach 1 t here...

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

Just a quick mention here. _Quinkana_ seems to have
spawned at least one individual that hit the 1-2 tonne
mark. 

It was mentioned on the list way back when. I don't
know if it was ever published though. 

http://dml.cmnh.org/1995Dec/msg00057.html

Maybe we'll luck out, and these landlubbing crocs will
be one of the next features in Indiana University
Press's "Life of the Past" series. 

Somehow I doubt it.
________________________________________

*more snips*

> > Some of that material has been recently published,
> and
> > can be read about in Ralph Molnar's recent book on
> the
> > subject (Dragons in the Dust: The Paleobiology of
> the
> > Giant Monitor Lizard _Megalania_). He calculated
> that
> > the largest material suggested a 2.1 tonne (1.9
> metric
> > tonne) animal.
> 
> I understand that the recent publication of a weight
> of mere 160 kg is now 
> considered too low, but... how can estimates differ
> by a factor of 10...?

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

I think it has to do with the (fairly) recent
_Megalania_ finds, coupled with the trouble inherent
with estimating the weight of a critter known only
from "Shitty Little Pieces."

________________________________________

> > Young altricial birds grow at twice the rate of a
> > proportional sized sauropod (Erickson, et al
> 2001).
> > Yet this is also the time of their lives, when
> these
> > young birds are known to be ectothermic (see
> Chinsamy
> > & Hillenius [2004] for a substantial list of
> > references backing this up).
> 
> Fine, they are ectotherms, but _very_ tachymetabolic
> -- and actually we're 
> talking about metabolism here, not about
> thermoregulation. 

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

True, which is why it would be nice if people arguing
this stuff would stick to bradymetabolism vs
tachymetabolism, and not endothermy vs ectothermy. 

But, that's neither here nor there. I'm not sure how
tachymetabolic these baby birds are, but it certainly
seems like a good example of what one can accomplish
by using a tachymetabolism for something other than
heat generation. 

In fact, they remind me of caterpillars.

________________________________________


Said birdies are 
> just too small (and to little insulated) to keep a
> constant body 
> temperature, so they rely on their parents instead.
 
+++++++++++++++++++++++++++++++++++++++++

I don't know. That seems like a poor excuse. Yeah
those birds are tiny, but mice are that size, or
smaller. Yet they still retain an automatic endotherm
lifestyle. Well, much of the time anyway.

Though now I'm wondering if baby mice are ectothermic
too.

_________________________________________

> > It would appear that food availability, and
> nutrient
> > partitioning (rather than general metabolic rate)
> are
> > the prime factors in fast growth.
> 
> Yeah... and body temperature. 

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

Which can be kept elevated through more ways than just
using a souped up metabolism.

Jason 
 


"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer


                
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