Re: Dinosaurian Class

[William Hinchman <bsaurus@bellatlantic.net>]

T. Mike Keesey wrote:

> I'm not sure what the exact cladistic definition of Diapsida is, but it
> falls somewhere between Sauria (+Lepidosauria, +Archosauria) and the more
> inclusive Romeriida (+Sauria, -Chelonia). Romeriida is the sister group to
> Anapsida (+Chelonia, -Sauria).
> 
> See http://umbc.edu/~tkeese1/dinosaur/animalia.htm
> (mostly taken from thew on-line Tree of Life)
> 
> --T. Mike Keesey                                   

Isn't Diapsida's primary defining feature "Two Holes", which include the
Infra Temporal openings, and also the openings on top of the skull
bordering the pineal opening?  Diapsids fall (cladistically) between
Sauropsids (Reptilia) and the Archosauria.

        Amniotes
          Synapsids

          Sauropsids
            Diapsids
              Archosaurs

I have seen Anapsids placed as an outgroup to Diapsids, and also, as has
been discussed, a further modification/specialization of the diapsid
form.  Also strangely, many diapsids show a loss of the lower temporal
bar, opening the bottom of this hole, as in Pliesiosaurs.

I tried to look at the URL provided in your posting, but I get a not
found message.

Bill Hinchman

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