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Re: [Re: [science or non-science?]]
We seem to be in agreement that pigeonholing doesn't work. Again, I was just
trying to give examples of what have been traditionally "cold-blooded"
I'll check into those refs as this does seem interesting.
Kendall Clements <firstname.lastname@example.org> wrote:
> > Laminforms are endotherms for the same reason that leatherbacks are
> > endotherms. They're big, bulky and swim alot. They are functionally
> > endothermic.
> I disagree with most of the above. Lamnid sharks possess a range of
> vascular and metabolic features consistent with the maintenance of
> elevated temperatures: internalized red muscle, elevated red muscle
> temperatures, and retia behind the eyes and within the hepatic
> circulation. They are NOT endotherms because they are simply "big,
> bulky and swim a lot." Have a look at the following reference,
> and references therein: Block, B.A., J.R. Finnerty (1994) Endothermy in
> fishes: a phylogenetic analysis of constraints, predispositions, and
> selection pressures. Env. Biol. Fish. 40: 283-302.
> Similarly, leatherbacks are not endothermic just because they are
> big. Have a look at:
> Davenport, J., D.L. Holland and J. East (1990) Thermal and biochemical
> characteristics of the lipids of the leatherback turtle Dermochelys
> coriacea: evidence of endothermy. J. mar. biol. Ass. U.K. 70: 33-41.
> Large size no doubt contributes to endothermy in leatherbacks, but
> there's a lot more to it than this. Unlike other sea turtles,
> laetherbacks possess extensive peripheral blubber. They also have a
> rete-like arrangement of blood vessels at the proximal end of each
> foreflipper. Furthermore, the freezing points of storage lipids in the
> fat of leatherbacks are consistent with endothermy, but not ectothermy.
> I think the tags cold-blooded and warm-blooded are a major obstacle for
> productive discourse on animal metabolic physiology. All the recent
> literature suggests that most animals fall somewhere in between. For
> example, the vascular modifications seen in varanid lizards MAY enable
> them to achieve activity levels above those of many lacertilians.
> Further, monotremes such as the echidna do not maintain constant,
> elevated body temperatures. Our understanding of metabolic physiology
> is not helped by trying to force animals, including dinosaurs, into one
> pigeonhole or the other.
> Kendall Clements
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