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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
> 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