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Re: Mammal - Like - Reptiles ... info needed.



>
>For that matter, what is the current status of the pelycosaurs?  It seems
>to me that I had heard a couple of years ago that they were no longer
>considered a valid group, but I have continued to see them refered to since
>then.

Virtually all phylogenetic analyses of Synapsida show "pelycosaurs" to form
a paraphyletic assemblage.  We could have defined a monophyletic
Pelycosauria, but it would have been completely redundant with Synapsida.

The word "pelycosaur" is sometimes used as an informal morphological
descriptor, e.g. "Dimetrodon is a pelycosaur-grade synapsid."  This implies
a range of morphology, not membership in a taxon.  As such, it's no
different than describing Tyrannosaurus as a nonavian dinosaur.


chris



-=--=--=--=--=--=--=--=--=--=
Christopher Brochu, Ph.D.

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

cbrochu@fmppr.fmnh.org