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Re: Synapsids weren't reptiles?

On Sun, Jun 29, 2008 at 8:47 PM, Dora Smith <villandra@austin.rr.com> wrote:
> I am looking at an article in the March 2008 issue of New Scientist.   It's
> a discussion about missing links or something; I seem to be missing the
> first page.
> It says that synapsids "were once" called mammal-like reptiles, bot no more,
> "because synapsids are not reptiles -- the two groups evolved in parallel
> from a common ancestor".
> What was the common ancestor - an amphibian?

No, an amniote. The first amniote, which was neither synapsid nor
sauropsid, but was immediately ancestral to synapsids and sauropsids.
(The authors are probably using "reptile" to refer to some group
within _Sauropsida_, although arguably the term "reptile" should just
be abandoned.)

"Synapsida" is generally used to refer to the mammalian total group
nowadays (i.e., everything sharing closer ancestry with mammals than
with any extant non-mammal). Other names for this group are
"Theropsida" and "pan-Mammalia".

A preferable term for the paraphyletic group that used to be termed
"synapsids", "mammal-like reptiles", etc. is "stem-mammals" (i.e., the
mammalian stem group: the total group minus the crown group).
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039