Re: Dinosaurian Class

[Bill Adlam <wa105@mead.anglia.ac.uk>]

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).
>+--+--Anapsida
>   +--+--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.

>>Does this mean we're all bacteria?<g>
>  Bacteria exist on a different branch of the tree of life than do any
>other form of life, extant or extinct. The Tree of Life page has this,
>and so does Mike Keesey's Page.

I can't comment on either web site right now, but the first statement is 
definitely wrong.  eubacteria unquestionably share more recent common 
ancestors with Eukaryota than with archaebacteria/Archaea.  

>  Pretty much, we are derived from the most recent common ancestor of
>bacteria and all other life, with bacteria as the outgroup. This is to
>say, we are derived from a bacteria-like creature that is not,
>essentially, bacteria. Same for dinos, birds, etc.

Eukaryotes are (descended from) a symbiotic aggregation of at least two 
bacteria.  The cytoplasm+nucleus and the mitochondeia of a Eukaryotic cell 
are (descended from) different bacteria.  Some argue that microtubule 
organising centres were/are another.  Chloroplasts, where present, are yet 
another.

Cladistic assumptions break down when dealing with bacteria, especially 
eubacteria, because of horizontal gene transfers.  The same goes for 
viruses, if they are to be included at all.  bacteria should be separated 
for this reason, and not because they form a clade.

N.B. In the above, clades begin with a capital letter, grades lowercase.

                                                        All the best,

                                                                        Bill