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Re: [science or non-science?]
> Laminforms are endotherms for the same reason that leatherbacks are
> endotherms. They're big, bulky and swim alot. They are functionally
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.