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HOW TACHYMETABOLIC IS..?



Norm King wrote:

> Remember "How big is big?"  The following question can be classified in 
> the same taxonomic (generic?) group:  "How tachymetabolic is 
> tachymetabolic?"
> 
> I wonder how dinosaurs would have been originally classified if they were 
> extant?  

I think Norm has a valid point. It might be logical to assume that a
living animal is either (1) tachymetabolic or (2) not
tachymetabolic. But I have seen (recently on shark-l, amongst other
places) experts disagree over whether endothermic fishes are truly
endothermic or not: it's somewhat arbitrary. John McCosker has shown
that _Carcharodon_ heats it stomach to speed digestion, with that heat
then being maintained as long as digestion occurs (he got the sharks
to swallow thermometers). The ambient temperature of the shark is
raised by this process. I don't want to get into the complexities of
shark physiology and whatever implications it might have for
dinosaurs, but it's worth pointing out that the rationale here is
circular.

BTW, some time ago I said that Naked mole rats (_Heterocephalus
glaber_ - yes I memorised the name..) were ectothermic. John
McGloughlin (where is he?) spoke to a naked-mole-rat-expert (snigger),
and reported on the list that this ectothermy thing was probably
wrong. Well it's not. At a recent Canadian zoological conference, I
forget the names, one speaker spoke about metabolic strategies in
rodents, and described the ECTOTHERMIC physiology of the Naked mole
rat in detail. He also presented data on a marmot, I think it was from
Vancouver Island, and said that 'Essentially, it is ectothermic'. The
little critter basked in the sun to heat up, and lied down in its
shady burrow to shed heat.

No doubt a whole world of physiological surprises await us. It's well
known that some sharks generate internal heat. Some of the scombroid
fishes (tuna, swordfish etc.) heat up their eyes and brains (did
thunniform ichthyosaurs do likewise?). Tree snakes can have higher
blood pressures than mammals, and monitor lizards can run around and
recover quickly from exercise. A surprising variety of birds go into
torpor. The Common poorwill (_Phalanoptilus(?)  nuttali_) truly
hibernates, while hummingbirds, swifts, mousebirds, manakins, sunbirds
and others undergo torpor if necessary. The Red panda (_Ailurus
fulgens_) apparently needs sunlight to metabolise (I want to learn
more about _that_!). Leathery turtles (_Dermochelys_) maintain
temperatures high relative to their environment (implications for
_Archelon_?). And as for bone microstructure...

There's a paper in the new Halstead tribute volume that describes some
kind of LAG in a small theropod. The critter seems to have slowed
right down toward the end of its life (metaphorically that is..).

Oh, and personally I think cuttlefish are smarter than any feathered
dinosaur.

["Impressive!  Most impressive!" -- MR]
"You'll find out I'm full of surprises"

DARREN NAISH