Re: Warm bloodedness in archosaurs before dinosaurs

[Stanley Friesen <sarima@ix.netcom.com>]

At 09:03 PM 6/17/97 -0700, Joshua Dyal wrote:
>...  From Bakker's book, I had almost gotten
>the impression that the thecodonts must have mostly been endothermic,
>but to my surprise, I don't see how that can be.  The reason is that 
>the crocodilians are very high up on the cladogram, cutting off at 
>least half of the thecodonts.  I suppose it is possible, especially
>if warm-bloodedness were "new" to the archosaurs, that crocodilians 
>could have dropped their metabolism back to ectothermic levels.

It doesn't even have to be all that "new" to be lost, in my opinion.  Being
endothermic is not always such a great thing.  It is expensive. So I could
well see an aquatic ambush predator, like modern crocs, losing endothermy:
after all, water is a fair temperature buffer on its own, and an ectotherm
need not catch as much prey.

In short, it is not at all out of the question for endothermy, or
proto-endothermy, to be plesiomorphic for the post-proterosuchid clade (I
forget its name), and lost in eucrocodilians (the modern sort), or perhaps
in mesocrocdylians (where they apparently returned to the water).

--------------
May the peace of God be with you.         sarima@ix.netcom.com
                                          sfriesen@netlock.com