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Re: Turtles and Crocodylians are not Reptiles - no? What are they?



On Wed, Jul 23, 2008 at 9:26 PM, Tim Williams
<twilliams_alpha@hotmail.com> wrote:
> I would say the number of clades is indeed a limiting issue.  Squamata, 
> Sphenodontia, Crocodylia and Aves represent just a fraction of
> the total sauropsid diversity that has ever existed.

Sure. And all fossil represent only a fraction of diversity that had
ever existed too. Few taxa could be more problematic if we have much
homoplasy.

> But for any gene, how do you know a priori which particular sites are 
> informative?

After aligment, if there is no variation there it will be
plesiomorphic to the group.

>  I'm not sure I understand you here.  I'm also not sure what you mean by 
> "fossil DNA", which you mention below.

My fault here. Normally "fossil" DNA reffer to a conserved DNA
sequence - somewhat molecular fossil - it could help in somecases. But
what I've meant is what Boehm said: DNA preserved in fossil.

> The most recent morphological/fossil data place whales near the base of the 
> Artiodactyla.  The analysis of Thewissen &c from late
> 2007 places Cetacea as the sister taxon to the Raoellidae, a group of aquatic 
> basal artiodactyls.  Thus, although the Cetacea come
> out as artiodactyls, they are not at all close to hippopotamids, and are in 
> fact outside the crown Artiodactyla.

Closer to hippos thant to mesonychids anyway.

> I reckon a similar situation will emerge with turtles (Testudinata): the 
> molecular analyses tend to place them inside or next to the
> Archosauria; older morpho/fossil analyses put them in an anapsid clade that 
> is outside the Diapsida; but new fossil discoveries will
> consolidate a position for the turtles somewhere in between, i.e. inside the 
> Diapsida as either basal lepidosauromorphs or as
> non-saurian neodiapsids.

Perhaps. Or it could place then near Archos. Vert paleontologists of
the world: go chase that fossil! : )

[]s,

Roberto Takata