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Re: feathers, hair and Compsognathus



At 08:24 AM 10/22/96 +0930, Jeff Martz wrote:
>     Not being up on my basal reptile phylogeny, could someone explain
>to me exactly why reptiles are now considered to be a paraphyletic
>group?
        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).

I assume this means that thier earliest common ancestor was NOT
>something that shared the traits that has caused scientists to group
>"reptiles" together.
        The traits which caused scientists to group them together were
symplesiomorphies.  The "Class Reptilia" was part of a different time, when
paraphyletic taxa were acceptable (well, ok, so they still are to some
workers. Some very influential workers, I should say...).  Changing
methodology in systematics has required the taxon to be redefined.  As far
as I can tell, serious cladistic practitioners do not like abandoning old
taxa if at all possible, so, while we can all feel that the taxon should be
pitched as confusing, it has merely been redefined into a meaningful
monophyletic group.

>What was this common ancestor, and how was it
>different?
        Boy, it would be nice to know that...
        :)
        Wagner
+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
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