[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Chelonians and Small et al's Archosauromorph



> suggests) or the  eureptile clade (s DNA analysis 
> suggests, though of course we have no 
> parareptile DNA).  According to one of the experts
> on this, Dr Robert  Reisz, we simply do not have 
> enough evidence to resolve this right now (or 
> so he told me).

Molecular data seem to give an emphatic support to the
position of turtles with extant archosaurs rather than
with the living lepidosaurs. With less confidence it
also suggests that the sphenodon is an archosaur
rather than a lepidosaur. Since there is very
probability that the extant diapsids are polyphyletic,
we have to accept this findings as implying that
chelonians are eureptiles and not parareptiles. 

Also one has to keep in mind that the times are
changing. Long ago the amount of sequence data was
relatively small and was susceptible to various
vagaries of molecular phylogenetic methods. However,
now the sequence data is fairly abundant and the
chance that there are convergences over hundreds of
sites is low. Hence any day sequence data is superior
to morphological data in phylogenetic reconstruction.
So turtles are likely to remain in archosauromorpha
for good. Hence it is the morphologists who need to
recaliberate their analysis. 

Some time ago Michael Lee had written a paper claiming
that molecular data should be given equal weight a
morphological data, but he was clearly missing the
point that convergence over hundreds of sites is not
probable in the current models of sequence evolution. 

So we need to chase the origins of turtles within
archosauromorphs rather than elsewhere as Reisz and
Lee had done in the past.

Like tyrannosaurs, turtles had less derived ancestors
too.
-EA

__________________________________________________
Do you Yahoo!?
New DSL Internet Access from SBC & Yahoo!
http://sbc.yahoo.com