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Re: synapsids are reptiles
I would agree with most of what Alberto said. I would only add that
since turtles are probably diapsids which reversed back into an anapsid
condition, defining Reptilia as a clade was a very bad idea in the first
place (and for other reasons as well, as has been often pointed out).
Reptilia has little (if any) value as a clade, so I hope cladists will
just abandon that idea, and let the rest of us use Reptilia in its
traditional (paraphyletic) sense. A number of cladists on this list have
already advocated abandoning a clade Reptilia.
And given the probable amniote nature of diadectomorphs, I proposed
here a month ago (DML, March 4th) that Order Diadectiformes be placed inside
of Reptilia (rather than as the sister group immediately outside of
reptiles). The cladistic topology remains the same.
As for the term "synapsid", I prefer to avoid using that term in a
taxonomic sense since it means two different things. It was redefined as a
clade to include mammals, so its traditional usage as a paraphyletic group
(pelycosaurs + therapsids) was compromised (just as with Reptilia). I'll
fight for the traditional paraphyletic usage of Reptilia, but have given up
on "Synapsida" (we have to choose our battles since there are so many of
The traditional usage of Amphibia is also worth fighting for. Whether
one wants to put diadectomorphs in Class Amphibia or Class Reptilia makes no
big difference to me since they were making the transition to basal amniotes
(i.e. basal reptiles, in the traditional sense). However, if diadectomorphs
are basal to the "synapsid" clade, then I would insist that they be
recognized as reptiles (not amphibians). An Order Diadectiformes as the
basal clade of Class Reptilia seems the best current option and predict that
it will remain in that position (thus promoting stability).
------ Ken Kinman
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