Re: Part 2: Terramegathermy (becoming longer again...)

["David Marjanovic" <david.marjanovic@gmx.at>]

> 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.

There could always have been a counter-current heat exchange system in long,
thin tails (thick ones are not so much of a problem IMHO), like in bird
feet, no? (If it was necessary.)

> 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.

Well, birds _normally_ have nearly double resting metabolic rates of
placental mammals. I have found numbers at the library in a book on
marsupial biology, have yet to copy them.

> > 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?).

My post, a short summary of that article, is
http://www.cmnh.org/fun/dinosaur-archive/2000Sep/msg00622.html. The ref is a
few "prev by thread" ahead.

> 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.

There are people, most prominent HPs Thomas R. Holtz & GSP, who think
otherwise AFAIK... I'll leave it to them. Just so much -- they all have long
legs, long distal limb segments (tyrannosaurs are arctometatarsalian), and
advanced dromaeosaurs have short metacarpals, so that HP GSP has suggested
"they sacrificed speed for agility" somewhere in
http://www.dinosauria.com/jdp/jdp.htm (can't find it now, and my brother is
waiting... :-( )

> > 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.

Because they have evolved the famous gular pump that allows them to breathe
during running. Crocs have the famous hepatic-piston pump for this, and
ornithodirans apparently had neither, instead they evolved erect stance.

> As for dinosaurs, they inhereted their erect stance from an erect
> ancestor

I simply claim that all Ornithodira were tachymetabolic, -aerobic, endo- and
homeothermic. =8-)

> and I know of no small archosaur (even _Compsognathus_ is big by
> extant standards).

A nonavian small archosaur? There is an unnamed coelophysid from Nova Scotia
as big as a blackbird (20 cm long)... and there are always juveniles!

> Even small crocs (which may or may not stand erectly,
> not that it matters much since crocs descended from erect ancestors)

Depends on whether or not Sphenosuchia is paraphyletic.

> aren't all that small.

Croc hatchlings?

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

Always a good idea... through unsatisfying... :-(

> 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,

Off the top of my head, *Austrosaurus* (Titanosauria, AFAIK) and
*Rhoetosaurus* (possibly Euhelopodidae, I just wonder how it got to
Australia from Asia, even if *Tehuelchesaurus* turns out to be related)

> and how cold were these polar
> nights?

Around 0 °C AFAIK. Months of darkness don't allow for much more.

> > > 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.

See above.

> > 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).

This implies that the arms were capable of quite some lateral excursion. Who
can enlighten me about ornithischian shoulder joints? :-)

> The forearms [legs] in all large theropods
> wouldn't allow for this type of quick turning, which would slow them down.

Well... Are recent ratites capable of quick turning? And were phorusracids
(many of which were highly cursorial)?

> 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.

That's news to me... Quite widely accepted, AFAIK, is today that gracile
*Australopithecus* and early *Homo*/*Kenyanthropus* did a lot of scavenging
(bone marrow is good for the brain!), running after the vultures to get
something before the lions and hyenas came...
        Slow tyrannosaurs? Someone has calculated offlist (last December
IIRC) that *T. rex*, when walking with 2 steps per second, already reached
36 km/h...

> 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.

In allosauroids, but not tyrannosauroids -- the latter are built for
terribly strong biting.

> > 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

It did. In the _Oligocene_ and again in the Mio-/Pliocene. Not earlier.

> and/or foraging
> distances required much longer periods of high energy flapping.

Difficult to imagine for shore- and small land birds, IMHO...

> Heck, I
> wouldn't mind knowing why early mammals developed L.C. endothermy as well,
> especially considering the warm climate that they were in.

It seems that this adaptation occurred much earlier, somewhere among or at
the beginning of the "therapsids". I am, however, badly informed about the
evidence here.

> > > 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?

Well, a tiger is 3 times as heavy as an ora, but requires 19 times as much
food, and 1/3 of a tiger, as heavy as an ora, still requires 5 times as much
food and not the same amount. Thus, the predator-prey ratio is quite
different, the tiger falling among endotherms and the ora among ectotherms.
Right?

> > > 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?

1. No, because there is still quite a considerable difference between damned
good reptiles and mammals.

2. Why not? Birds have much higher resting metabolic rates than placental
mammals on the average...