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Re: feathers, hair and Compsognathus



At 09:07 AM 10-24-96 +0930, Jonathan Wagner wrote:

>>         The origional Class Reptilia (Linneaus) was paraphyletic, as it
>> includes early synapsids but not the mammals, and early Sauropsids, but not
>> birds.  As it stands now, Reptilia has been redefined so that it is
>> monophyletic, but excludes the "mammal-like reptiles" and includes the
>> birds.  For some perspective, see the Tree of Life homepages (sorry, URL not
>> handy, e-mail off-list me if you can't get it).
>
>      Does this mean that mammal like reptiles are NOT descended from
>animals with reptilian traits that got these reptilian traits from a
>same common ancestor that reptiles got thier reptilian traits from?
>Exactly why are synapsids excluded?

The problem here is that "reptile traits" are plesiomorphic.  Ectothermy,
scales, sprawling posture, amniotic egg laying, etc.  are all features
shared by the common ancestor of amniotes.  Reptilia on the other hand is
defined by the last common ancestor of turtles, lepidosaurs, and archosaurs.
Just because these taxa retian these traits does not indicate ancestry.

David J. Froehlich                              Phone: 512-471-6088   
Vertebrate Paleontology Laboratory                Fax: 512-471-5973
J.J. Pickle Research Campus
The University of Texas, Austin, Texas 78712