Re: [Re: [science or non-science?]]

[archosaur@usa.net]

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"
creatures.

I'll check into those refs as this does seem interesting.

Archosaur J






&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&7

Kendall Clements <k.clements@auckland.ac.nz> wrote:
> Re:
> 
> > 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
> k.clements@auckland.ac.nz


Jurassosaurus's Reptipage: A page devoted to the study of the reptilia

http://members.tripod.com/~jurassosauridae/index.html

____________________________________________________________________
Get free e-mail and a permanent address at http://www.netaddress.com/?N=1