[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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.
>Dept. of Geology
>University of Maryland
>College Park, MD 20742
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