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

[archosaur@usa.net]

After *finally* finishing this e-mail, I've realized that point by point
discussions are going to blow away the bandwith. I think I'll stick to
installments next time.

Very short:

> ...Migrators must be tachymetabolic. InMRs probably aren't enough to >
surpass 5 tonnes. Fluctuating MRs can't be exploited very far because > hard
heart work must be sustained to prevent torpor. 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, 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?

___________________________________


> "Reptiles" grow too slowly to evolve giant sizes, while populations > of
megamammals are small and unstable and can't easily be refilled by >
reproduction.

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

I think HP Darren Naish already mentioned the mammal bit, so I won't touch
that. Good thing too, since I don't know enough about mammals in that area.

As for reptiles, how big do you want. We have huge snakes, turtles, crocs and
lizards. Ancient reptiles were huge too. _Deinosuchus_ was easily _T.rex_ size
and _Testudo altas_ ranks up their with the really big mammals and the medium
sized dinos. 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. For now,
sauropods are the only animals capable of growing to sauropod size.

I'll touch on growth rates below.

____________________________________



> Desert elephants never overheat, so HiMR sauropods shouldn't have > either.
Therizinosaurs, and maybe early dinosaurs with small ilia, > probably had
InMRs like giant sloths. Sauropods didn't always carry > their necks
horizontally and so had to pump blood up all
> the way which requires more blood pressure than a bradymetabolic > heart can
produce. Gigantothermy would require unreasonable amounts > of fat. Sauropods
didn't have feeding problems.

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

What's an unreasonable amount of fat? Sauropods were many times larger than
the largest leatherback and they never dealt with temperatures as extreme as
those the leatherback faces. If they did have the same proportion of bodyfat
that _D.coriacea_ has then I'm sure they would overheat, but we're talking
about huge animals in the tropics. I believe minimal bodyfat and gigantothermy
could still go hand in hand there.

_________________________________

Very long:

> "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?

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?

_____________________________________________________

> There once was an article called, IIRC, "An alternative to           >
hot-blooded dinosaurs: the happy wanderers" or something like that.  > Well,
nothing of the sort:

> "*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). This is    > true of large as
well as small animals. The 2-7 km/h walking speeds  > observed in elephants
for example (Fig. 5) are easily achieved       > aerobically. 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."

> 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." I'll see if I can
get some of that more dependable data. I mean it has been about 70 years, so
I'd imagine that someone must have done a study or two in that time.

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). 

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.

_Geochelone nigra_ is also known to migrate both for nesting purposes and for
food (again highlands to lowlands stuff).

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

At anyrate there are migrating reptiles.

______________________________________

> Fig. 5 plots the speeds of elephants and rhinos (from videos),       >
ornithopods +theropods, ceratopsids, nodosaurids and sauropods       >
(estimated from trackways), which all begin at 2 km/h upwards, and   > "the
low sustained walking speeds predicted by the reptilian aerobic > metabolism
of a cruising leatherback sea turtle" under 1 km/h.

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

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.

____________________________________

> "Galloping rhinos do not have higher resting MRs than slower         >
elephants, although their exercise MRs may be higher. The most > gigantic
extinct mammals were 10 to 20 tonne, HiMR proboscideans and > indricotheres
with long striding legs [...]. Giant extinct edentates > and marsupials with
heavy awkward limbs never exceeded about 5 tonnes > [...], and these rather
sluggish beasts probably had InMRs like their > living relatives (McNab,
1983). If so, land animals much over 5 onnes > may need HiMRs.

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

How much do we know about _Megalania_? Did it hit 5 tonnes?

________________________________

*snip*

> *Growth and reproduction. -* Fig. 6 shows that land reptiles grow > more
slowly than birds and all but a few terrestrial HiMR mammals > (Case, 1978).
Note that the divergence between terrestrial reptilian > and mammalian growth
rates _increases_ _with_ _size_; this negates > the premise of gigantothermy
that the growth rates of land giants > should converge towards a common
level."

> Fig. 6 is impressive. Growth rates in g/day are plotted against body > mass
for reptiles, marsupials, placentals in general, whales, > ungulates,
elephants, hippos, altricial and precocial birds, a > hadrosaur nestling, a
hadrosaur (at what age?), a ceratopsid and the > "[m]inimum growth rates
needed for giant sauropods to reach sexual > maturity at 1/3 adult mass". The
area occupied by placentals touches > that of reptiles at small sizes but
diverges clearly at large ones, > small marsupials overlap with reptiles while
bigger ones overlap with > placentals and middle ones are in between,
cetaceans diverge even > more strongly, rhinos, hippos, hadrosaurs and
ceratopsids are on the > lower border of the ungulate range, elephants are
below, the minimum > for sauropods lies on the extrapolation for elephants and
the > hadrosaur nestling on that of the upper border of the range of >
altricial birds, which have the highest growth rates.

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

Interesting; what reptiles were used in the diagram?

Were they crocodiles?

If so what species and from what locality? 

Were snakes used? 

Varanids?

Iguanas?

Turtles?

The species studied is going to affect the statistics. One of the more
annoying thing about bradymetabolism is that growth rate is highly dependent
on the amount of available food (unlike L.C. endotherms which grow at the same
rate regardless of available food). 

For instance, if the animals are Nile crocs from the Grumeti (sp?) river then
they are going to look extremely slow growing since these crocs have adapted
to one huge meal a year. If they are crocs from a more populated region, the
growth will again look different. 

If it's a temperate reptile the growth will go slower than if it were a
tropical reptile. 

A favourite example of mine is the Burmese python (_Python molurus
bivitattus_) which has a high growth rate in the wild (from a 22" hatchling to
a 9ft juvenile in one year) but can take 6 to 8 years in captivity to reach
the same size if not fed properly. 

So the growth statistics are going to skew one way or the other depending on
the test subjects used.


____________________________________


> "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.

____________________


> 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 because
they keep banging into the walls of their cages, cutting them up and causing
severe, life threatening (and often life taking) stress.

I take it that this was more do to the running leatherback theme :)

_______________________


> 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). Extant crocodilians grow slow
(again depending on environ and species) because of the niche they occupy,
which is often one where months may go by between meals. As such, croc
metabolism is used to eating a lot fast and storing for months at a time.

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 don't suppose anyone has done any bone histology studies on terrestrial
crocs (you know, for what they're worth)?

_________________________________

 Big ungulates, rhinos, elephants, and whales fit these characteristics
(Owen-Smith, 1988). [There is a recent New Scientist article "The old man of
the sea" that says that the oldest whale caught was 211 years old, based on
the aspartic acid racemization in its eye lenses.] Note that the more gigantic
an animal is, the higher the rate of growth must be in order to keep the
juvenile stage and lifespan within reasonable limits. [Whales fit this, Fig.
6.] 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_, _Deinosuchus_ & _Purussaurus, many rauisuchians, mosasaurs,
elasmosaurs, _T.atlas_, etc.) If they were all tachymetabolic L.C. endotherms
then we are looking at a lot of secondarily ectothermic, bradymetabolic
descendants.

________________________________

A problem with being a tachyaerobic giant is that each adult consumes
large amounts of food, so the total adult population size is rather small
(Farlow, 1993; Paul, 1994). [...] In general, small populations are less
stable than larger ones over geological time. [...] Under optimal natural
conditions megamammals can expand their populations about 6-12% per annum
(Owen-Smith, 1998). These modest rates of population expansion have allowed
megamammals to evolve moderately gigantic masses during the Cenozoic. Large
reptiles lay large numbers of eggs, but their slow growth and generational
turnover hinders their ability to exploit their rapid reproduction to evolve
giant dimensions. 
++++++++++++++++++++++

Again, this is species specific and we have had numerous large,
non-dinosaurian, reptiles.

_____________________

And now into biomechanics and myology:

"The early dinosaur condition was not a very satisfactory one because
the full potential of the long erect legs could not be realized until the size
of the ilium and the leg musculature expanded to avian-mammalian proportions.
This is the condition observed in 'longoschian' [why -o- instead of -i-, and,
again, why the ischium?] theropods, therizinosaurs, ornithischians and
sauropods of all sizes [...]. 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 ;)

______________________

*snip*


[...] Figure 5 [...] proves that megadinosaurs walked in the same fast
lane as HiMR megamammals, not in the reptilian slow lane. Only the bizarre
advanced therizinosaurs [...] had awkward feet suggestive of InMRs like those
of giant sloths. It is widely agreed that some megadinosaurs migrated long
distances (Currie & Dodson, 1984; Horner & Gorman, 1988); such journeys
demanded high aerobic capacity.

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

Komodo dragons don't walk in the slow reptilian lane either, yet they are
bradymetabolic. There is no doubt that high aerobic capacity is required for
long distance, overland travel, but we have many bradymetabolic animals that
accomplish this without resorting to a tachymetabolism. I don't see why
dinosaurs would have to either.

_____________________________

*Megadinosaurs were not weak. -* Over the years it has been asserted
that sauropods could not move on land, rear up, feed HiMRs, or pump blood up
their long necks, that large dinosaurs had limited breathing capacity and
moved slowly, and that big theropods were mere scavengers - it is amazing that
the 1-100 tonne weaklings survived at all! Examining the structure of
megadinosaurs reveals strong animals of high aerobic capacity and great
athletic ability. Figure 1 shows that at any given size, megadinosaur
skeletons (especially their vertebral columns) were more strongly built than
those of megamammals.

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

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. 

Komodo dragons were once (and still are) considered to only be scavengers, but
thanks to more in depth studies done on them by Auffenberg et al, not only do
we know that they were accomplished hunters, but they had a hunting activity
(i.e. predator/prey ratio) that was equal to tigers. 

Not bad for a damned good reptile :)

______________________

*snip*

*SUMMARY AND CONCLUSIONS*

[...] The giant dinosaur's fast growth was possible only because the
juveniles had fast running metabolisms, and dramatic fall offs in MRs with
maturity are not only contra-indicated but may have been reversed in tall
sauropods" because cardiac work seems to increase faster than body mass with
size.

*snip*

But, contrary to the argument that many dinosaurs had some form of
transitional metabolics, the anatomical evidence shows that this condition was
limited to early brevischian dinosaurs [...]. There was little or nothing
reptilian in the energetics of big bodied and/or big hipped dinosaurs. [...]
We find the recent tendency to cite marine and captive reptiles as primary
analogs for dinosaurs as unconvincing as it is perplexing. Giant dinosaurs
were not good reptiles, or damned good reptiles. They were marvelous
archosaurs whose anatomy and aerobics converged with megamammals. It is only
logical that the closest living models for extinct land giants are living land
giants with aerobic metabolisms, circulatory systems, and growth patterns
suitable for terrestrial gigantism under natural conditions. [...]

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

I'd hardly say all that. The energetics in extant reptiles are still being
understood and we have many prehistoric reptiles that reach dinosaurian
proportions yet have not been considered candidates for L.C. endothermy. Why
shoud dinosaurs be any different?


and one more *snip*

Wow that was a lot. Thanks for the info; I'll still see if I can get my own
copy, if only so I can look at the figures.

Jura

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

http://reptilis.net

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