Re: [Part 2: Terramegathermy (very long, too)]

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

> After *finally* finishing this e-mail, I've realized that point by point
> discussions are going to blow away the bandwith.

The post that started this thread had 24 KB... is this so much? :-|

> > [...] Dinosaurs grew as fast as
> > birds & mammals; the difference of reptilian and bird & mammal growth
> > rates increases with size, rather than disappearing, as advocates of
> > gigantothermic megadinosaurs assume.
>
> > I don't get it. If we keep finding conflicting histological examples
with each
> > species studied,

Do we? The most recent articles I know all agree that the species studied
grew very fast.

> how can we really know how fast any dinosaur grew? Is there
> anything else dino growth rates are being based on, other than bone
> histology?

Not much. Mainly the argument from generational turnover: *Deinosuchus*
needed 50 years to reach 10 m. If a sauropod would already have been 100
years old when reaching _adult size_ (recent articles say 10 years based on
histology), the populations would have been endangered all the time, and the
fossil record would look different (contain far, far less adult sauropods
and more younger ones).

> As for reptiles, how big do you want.

Over about 1 tonne and terrestrial.

> We have huge snakes, turtles, crocs and
> lizards.

All stopping at or near 1 tonne, AFAIK.

> Ancient reptiles were huge too. _Deinosuchus_ was easily _T.rex_ size

Semiaquatic, and only 10 m long (for decades it had been estimated at 15 m).

> and _Testudo a[tl]as_ ranks up their with the really big mammals and the
medium
> sized dinos.

I don't know how much is known of it. P&L's Fig. 1 shows a silhouette with
no bones that is as big as a 1.5 t rhino, if you forget the latter's longer
legs and much bigger neck and tail. It is about 1 m high and 2 m long. This
is far smaller than the really big mammals (say, elephants or indricotheres)
and among the rather small dinosaurs (except if you count by small, medium,
large, very large, gigantic, enormous, humongous, ...)

> Admittedly we don't know of any reptiles that grew to sauropod
> size, but then we don't have any mammals or birds that do either.

P&L suggest why -- because the populations of adult animals of sauropod size
are very small, they must have crashed from time to time, leaving the young
alone. This is a problem for mammals and many birds, which depend heavily on
their parents.

> For now,
> sauropods are the only animals capable of growing to sauropod size.

Sure. P&L say this must have a reason, and write they've found it.

> > Gigantothermy would require unreasonable amounts of fat.
>
> What's an unreasonable amount of fat?

The amounts that occur in domestic animals and Spotila et aliorum
calculations of gigantothermic dinos.

> Sauropods [...] never dealt with temperatures as extreme as
> those the leatherback faces.

The other way round, as HP Randy Irmis has pointed out.

> > "Long anterior airways pose a respiratory problem because they hinder
> > ventilation of the lungs. Even so, sperm whales (Fig. 4) inhale enough
air
> > through long anterior airways to sustain HiMRs with modern oxygen
levels.
> >
> > This is true despite the small size of their lungs, the lack of
> > respiratory air-sacs, and the need to respire during brief periods at
the
> > surface between long dives."

> I apologize for this but; didn't P&L just say how weird and inappropriate
it
> would be to use whales as basic dino comparisons? And aren't they doing
that
> right now?

They are forced to doing this :-] , because nothing else has a trachea
anywhere near as long as a sauropod's. The anterior airway of a sperm whale
is 7 m long, because the blow hole is located rostrally on an enormous head.

> Anway, one must also take into account that sperm whales, like all
aquatic,
> non-amphibian tetrapods, spend a large chunk of their time not breathing.
As
> such, their bodies are going to have adaptations to deal with low oxygen
> supplies. Therefore is it wise to use a sperm whale's respiration regime
as a
> comparison to sauropods?

It is not wise. It just shows that in principle it is possible to live with
nostrils and lungs 7 m apart. Of course, many sauropods surpassed this, and
had air-sacs, while the whales have adaptations to low oxygen supplies. In
the absence of any better analog, it is the wisest thing available, I'd say.

> > *Cruising and migration. -* In order to forage long distances on a
> > daily basis, or to migrate very long distances on a yearly basis,
> > sustained walking speeds should be above 2-3 km/h. Because moving on
> > land is energy expensive, high aerobic capacity is needed to power
> > such high cruising speeds for many hours (Bennett, 1991). [...] Although
> > swimming leatherbacks cruise at 3-5 km/h, the sustainable aerobic
capacity
> > of leatherbacks can power walking speeds of only 0.5-0.8 km/h (Fig. 5).
The
> > long migratoins[*] of leatherbacks are possible only because they swim
so
> > cheaply, and exploit favorable currents [...]. Anaerobiosis does not
produce
> > power long and efficiently enough to power high walking speeds, so
> > calculations that bradyaerobes can migrate farther than tachyaerobes on
land
> > (Spotila et al. 1991) are incorrect, and no land reptile migrates."

* Yeah! I've become normal! I've made a TYPO without noticing it! ;-)

> > Aren't there some "exceptions that prove the rule"? They've slipped my
> > mind...
>
> There sure are :)
>
> Another on the list has already mentioned rattlesnakes. I'm not sure of
their
> exact migration distance, I only know that Laurence Klauber wrote in his
book
> Rattlesnakes, that they "rarely travel over a mile" to reach their dens,
> though he also notes that "dependable data are not at hand."

A mile is not comparable to, say, what happens in the Serengeti.

> Besides rattlers, we also have Galapagos land iguanas (_Conolophus_ sp)
and
> other lizards that are known to travel large distances to reach their
nesting
> grounds (_Conolophus_ females go from the Galapagos lowlands all the way
to
> the top and then inside the calderas of extinct volcanoes to deposit their
> eggs).
> [...]
> _Geochelone nigra_ is also known to migrate both for nesting purposes and
for
> food (again highlands to lowlands stuff).

Same...

> Auffenberg is his 81 study of _V.komodoensis_ states that "adults may move
as
> much as 10km/day..." Now, barring the fact that this is yet another island
> species I'm using, that is still a pretty hefty distance.

This is becoming more interesting, but it is still much less than 2 -- 5
km/h...

> Crocs are no to migrate long distances over land to find new waterholes,
> though it isn't as regular as the other examples.

How far?

> At anyrate there are migrating reptiles.

True, and this contradicts the last 5 words in the above quoted paragraph,
but there are no far-migrating terrestrial reptiles (those that need fast
walking speeds), are there?

> Auffenberg clocks normal walking Komodo monitor speed to be 4.8 km/hr,
which
> easily falls within the range of the dinosaurs and pachyderms mentioned.

For how long can a Komodo monitor walk? An hour? :-/

> How much do we know about _Megalania_?

I don't know. All I know is that not much is known...

> Did it hit 5 tonnes?

Surely not, P&L put it at 1 tonne.

> > Fig. 6 [...]
>
> Interesting; what reptiles were used in the diagram?

"Data for modern animals in part from Case (1978)." This is all I can find
concerning that. Fortunately, we can ask one author...

> > "The inability of bradyaerobic juveniles with low foraging speeds and
> > ranges to gather enough food is one reason they grow slowly.
>
> Again, this is a species specific issue.

Sure?

> > It has been suggested that elevated growth rates of farm-raised
alligators
> > and captive leatherbacks show that reptiles can grow rapidly.
>
> Um, what captive leatherbacks? Leatherbacks can't be kept in captivity
[...]

No idea. I can only quote.

> > Raising alligators is an energy expensive and labor intensive
proposition
> > that involves providing idle reptiles with large quantities of food
> > (Grenard, 1991). The relevance of captive and[/]or aquatic reptilian
> > juveniles to natural land conditions is nil.
>
> I disagree; while it might not be viable to use captive growth rates to
normal
> wild ones, it does show that growth is highly dependent on available food
in
> many reptiles (tortoises might be exceptions).

The implication is that such lots of food aren't available in the wild, and
never were, so bradymetabolic dinos couldn't have grown big enough.

> But what of their prehistoric ancestors? Well there's a question eh, croc
> biology preadapts them (one could say) to a high energy existence. They
have
> an efficient gizzard digestive system coupled with xenomorph like stomach
acid
> that can even handle bone. They also have a four chambered (though
aquatically
> modified) heart and a diaphragm. None of these would be expected in a
> semi-aquatic ambusher, yet there they are.
>
> Of course these are more leftovers than they are preadaptations, but
> regardless it would seem that immediate crocodylian ancestors were more
active
> than extant ones. This probably means that they grew much faster too.

I'd rather say that fossil terrestrial crurotarsans were more like monitors,
that is, "good reptiles" with a hepatic-piston pump (whereas monitors have a
gular pump), but still rather bradymetabolic and slow-growing. The
thermophysiology of rauisuchians (vertical limbs!) is going to be very
interesting once it is studied at all...

> > We conclude that HiMRs are
> > necessary to grow more than 5 tonnes. The large size of some extinct
> > marsupials and edentates suggests that InMRs are sufficient to grow to
about 5
> > tonnes, and LoMRs can grow animals to only about 1 tonne.
>
> But we have numerous prehistoric reptiles that easily exceed 1 tonne
>(_Megalania_, [...] _T.atlas_

Not (much) over 1 t.

> _Deinosuchus_

Semiaquatic. And probably not much heavier either.

& _Purussaurus_,

What is this? How big was it? ... :-9

> many rauisuchians,

Over 1 tonne?

> mosasaurs, elasmosaurs, etc.)

Aquatic. Whale sharks reach 15 tonnes.

And now into biomechanics and myology:

> > Among megadinosaurs, the ilial plates of
> > tyrannosaurs are so large that a high endurance limb musculature
suitable for
> > chasing down large prey is indicated over ambush or scavenging habits.
>
> Great, now as long as the prey item doesn't make any sharp turns _T.rex_
will
> be set ;)

I don't understand this...

> Much of which I can certainly agree with; I just don't see why you need to
> shove them into the inefficient realm of tachymetabolism to achieve this.

Hm. Considering that tachymetabolism has not been selected against in birds,
mammals, and others, it must have some advantage...

> Komodo dragons were once (and still are) considered to only be scavengers,

"And still are"? Even though they're on TV every month?

> [...] they had a hunting activity
> (i.e. predator/prey ratio) that was equal to tigers.

1. Is this the same, hunting activity and predator/prey ratio?
2. From TV observations (not field observations, though...) I claim their
predator/prey ration is much higher than that of tigers. There are just lots
of them

> Not bad for a damned good reptile :)

Sure. But still not good enough to grow to *T. rex* size.

> Wow that was a lot. Thanks for the info;

No problem! :-)