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Re: Dinosaurian Class
Bill Adlam wrote:
> Jaime wrote:
> > It's: Amniota including Diapsida (crocs, dinos, birds, lizards) and
> >Synapsida (pelycosaurs, us) with the outgroup as Anapsida (your
> >favorite box turtle, for instance).
> > +--+--AMNIOTA
> > +--+--Diapsida
> > +--Synapsida
> This classification has now fallen out of favour. It is more likely that
> Chelonians are Diapsids which secondarily reverted to the anapsid state
> (their skulls are clearly heavily modified). Other anapsids are a
> paraphyletic mix of early Amniotes.
> I do not know the difference between Reptilia (new definition) and Diapsida.
The most recent reference I have ("Diversification of the Amniotes," Jacques
Gauthier, 1994) states it like this:
Amniota = Synapsida + Sauropsida
Synapsida = mammals and everything closer to modern mammals than to modern
Sauropsida = Mesosauridae + Reptilia
Reptilia = Anapsida + Diapsida
The article isn't clear on how Anapsida is defined. The text says "turtles and
everything closer to turtles than to saurians," where "Sauria" includes
lepidosaurs + archosaurs + a few minor groups. The cladograms say "turtles and
everything closer to turtles than to diapsids," with rather more critters
included in Diapsida than just the saurians.
There was a study a year or two back that suggested chelonians are not anapsids
but heavily modified diapsids, which would make a nice hash of much of the
Sauropsida, but that classification hasn't been generally accepted.