Re: Warm bloodedness in archosaurs before dinosaurs

[Jeff Poling <jpoling@dinosauria.com>]

At 09:03 PM 6/17/97 -0700, Joshua Dyal wrote:
>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.

   There's one piece of evidence you need to add to your dataset:

   Crocs current niche and physical configuration appears to be a secondary
adaptation.

   According to an article on my website (I believe it is "croc with erect
stance found") the first Crocodylians or Crocodylomorphs had a fully erect
stance, a four chambered heart and were wholly terrestrial.

   As they changed from terrestrial to semi-aquatic, probably both because
of the dinosaurs and the extinction of the phytosaurs, their physical
configurations changed to a functionally three chambered heart, ectothermy,
and a semi-sprawing stance.  Apparently the semi-sprawling stance still
allows modern crocs to gallop (observations of nile crocs) for short
distances showing their evolution from fully erect ancestors (as quadrupedal
dinosaur hind- and fore-leg proportions show their evolution from bipeds)
and their heart still is physically four chambered but "imperfectly" so
making it functionally three chambered (which apparently is an adaptation to
allow them to stay submerged longer).

   Somewhere in the paleo ring is a website dedicated to crocs.  You might
give it a visit.

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