Re: [Re: [Part 2: Terramegathermy (not too long :)]]

[archosaur@usa.net]

Ooh, this was very annoying. With the advent of the new Yixian fuzzball, I
never got these last two posts. In fact if it weren't for HP Adam
Britton's original response to one of them, I never would have even known
that they existed.

I do so hate it when that happens.

Oh and since these are basically short responses, I decided to consolidate
the two (reference posts included).

From: http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00550.html

___________________________________

> Long-bodied? I wouldn't say that. Sure, they have long, thin tails, but
> many recent birds have extremely long necks in exchange. As long as
> those elongated body parts are insulated, I don't see any problem (and
> even if, there would still be the warm mesozoic climate), and never
> mind  bird feet, which are "insulated" only by a counter-current heat
> exchange system -- even tiny birds can walk on ice for long periods!

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

The basic dinosaur and archaeoptergiforme bodyplan stands in stark
contrast to those of mammals and birds. Whereas all mammals and birds
maintain the short, thick body so as to limit heat loss, early versions
had much longer bodies, complete with long, thick tails, which don't bode
well for an L.C. endotherm.

As I mentioned, we do have weasels, but their metabolism requires them to
consume around twice as much as similar sized mammals. L.C. endotherms
*can* get long, but the energy costs of doing so seem to limit them to
only the occasional foray.

For more on this (and assuming that Chris doesn't mind me plugging his
book), I highly recommend Chris Laver's book: Why Elephants Have Big Ears
, which gives a very thorough look at thermophysiology among different taxa.

Again, as I stated, this evidence by itself, just like the RTs and the
LAGs, doesn't help much, since there is always an exception to the rule
(i.e. if chelonians weren't alive today, than by this mode of thinking
they would be L.C. endotherms). Together though, they are at least a
little telling of the possible physiology of dinosaurs (i.e. all the above
are used as examples of non-L.C. endothermy regardless of their
exceptions, and they are all found in these animals).

Since HP Adam Britton answered the first query I'll leave it be.

_______________________________

> 2. A pristichampsid was surely faster, but these were ambush predators
> (according to the in-depth research of the article about *Pristichampsus
> rollinatii* that has been mentioned onlist some months ago) --
> hyperanaerobiosis is a perfect adaptation for this. Many theropods
> weren't ambushers.

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

There was a pristichampsid reference on the list? I must have missed it.
Could anyone direct me to the post in question as I'd love to hear why a
"hoofed crocodile" would be considered an ambush hunter (how many ambush
hunters need hooves?).

As for theropods, I contend that most were ambush hunters. In particular,
the large theropods, which seemed to lack an effective turning ability.
Dromaeosaurs would appear to be different (though their legs suggest
otherwise) and probably could, at least, do long sprints.

____________________________________

> > to have "more erect" stances than most lizards (even Komodos hold
> > their legs a little more under than other lizards).

> Does anyone know about *Megalania*... ?

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

All I know is that we have a partial skeleton of it, but no mention of
what that partial skeleton entails.

_________________________

> But large size has appeared after erect stance, at least in
> dinosauromorphs. High activity, combined with the absence of a gular or
> hepatic-piston pump, may be a better reason. *Eudibamus* the Bizarroid
> Little Anapsid may also be such a case.

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

Ah, but varanids are highly active and still retain their sprawling
stance. As for dinosaurs, they inhereted their erect stance from an erect
ancestor and I know of no small archosaur (even _Compsognathus_ is big by
extant standards). Even small crocs (which may or may not stand erectly,
not that it matters much since crocs descended from erect ancestors)
aren't all that small.

Oh well, I suppose it would be best to leave this in the area of: "More
work needs to be done" for now.

From:

http://www.cmnh.org/fun/dinosaur-archive/2001Apr/msg00552.html

___________________________________

> > Better?

> No... unless polar sauropods evolved a different metabolism from others
> several times.

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

Why, how many polar sauropods were there, and how cold were these polar
nights?

________________________________

> > As for the carnivores, Auffenberg himself, mentions that
> > ambush predators seem to grow to very large sizes. This could explain
> > the large theropods [...]

> I disagree. Tyrannosauroids at least are built a lot like runners, and
> quite different from *Pristichampsus rollinatii*.

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

Maybe in the sense that _T.rex_ was bipedal, but other than that, I'd say
that the latter is more built for speed than the former.

__________________________________

> I don't think anything the size of *Edmontosaurus* or *Triceratops* can
> zig & zag, at least not faster than *Tyrannosaurus*...

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

Maybe, but do note that both of these herbivores have (or can have) four
legs on the ground, which increases stability a lot, along with
maneuverability. An _Edmontosaurus_ could come down on all fours while
running and use its forelegs to push off in a new direction (or to
stabilize itself upon turning). The forearms in all large theropods
wouldn't allow for this type of quick turning, which would slow them down.

I suppose  _T.rex_ could try just slowly, but continuously pursuing its
prey until it collapsed from heat exhaustion. Hey, it worked for early
humans. Of course, this wouldn't explain the structure of the skull and
jaw; both of which seemed made for torpedoing into prey items much like
how white pointers take out elephant seals.

Anyway, just some thoughts.

______________________________

> By this I meant, if early birds were bradymetabolic, why didn't recent
> birds keep that efficient adaptation?

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

Perhaps, because the climate of the earth got a lot colder and/or foraging
distances required much longer periods of high energy flapping. Heck, I
wouldn't mind knowing why early mammals developed L.C. endothermy as well,
especially considering the warm climate that they were in.

_____________________________


> > From: Behavioral Ecology of the Komodo Monitor.
> > Though there is great disparity in comparing the values for oras and
> > the large mammalian predators, when the latter are considered in
> > terms of the porportionate difference in predator size and waste
> > percentage of prey, the disparity is not nearly as great. Thus,
> > though the size ratio of an adult ora to an adult tiger is 1:3, the
> > ratio of the pounds of ungulate prey required per year for each is
> > 1:19. When percentage waste is considered it is 1:15 and when
> > poportionate predator size is considered it is 1:5.
> > As I said...

> These numbers fit my above claim, IMHO...

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

Care to elaborate on that?

______________________________

> > Not bad for a damned good reptile :)

> Still not good enough for a dinosaur! =8-)

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

Only if you are implying that dinosaurs had metabolism *higher* than mammals?


Jura


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

http://reptilis.net

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