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Re: Re: Warm Blooded vs. Cold Blooded

At 1:25 PM 9/12/95, th81 wrote:
>>        Ectothermy is the primitive condition in reptiles.  W/out evidence
>>to support the evolution of the derived condition (endothermy), the
>>primitive condition is assumed.
>This isn't quite using the extant phylogenetic bracketing method.  The
>extant ingroup, birds, are all endothermic.  As for outgroups, crocodiles
>are ectothermic, lepidosaurs are ectothermic, turtles are ectothermic, and
>mammals are endothermic.  As such, assuming either endothermy or ectothermy
>by phylogeny, rather than other evidence, is very weak.
>Thomas R. Holtz, Jr.
>Vertebrate Paleontologist
>Dept. of Geology
>University of Maryland
>College Park, MD  20742
>Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
>Fax: 301-314-9661

        Endothermy, as applied to both birds and mammals, is a blanket term
that describes two different and discrete forms of thermogenesis, not
thought to have arisen via a common ancestory (at least not thought so
anymore).  Since the biochemistry is different, you wouldn't consider
mammalian endothermy to be the same metabolic pathway (character in a
phylogeny), as avian endothermy.  Problem solved.

Jason J. Head
V.P. graduate student
Dept. of Geological Sciences
Southern Methodist University
Dallas, Tx. 75275