RE: New Limbed Cretaceous Snake

[John Scanlon <riversleigh@outbackatisa.com.au>]

Vidal and Hedges (Molecular evidence for a terrestrial origin of snakes.
Biology Letters 271: 226-229, 2004) used no ancient DNA and no data on
fossils to arrive at their conclusion.

They simply assumed that mosasaurs are most closely related to varanids.

A molecular phylogeny of squamates found varanids and other anguimorphs to
cluster with each other to the exclusion of snakes, from which (including
the extra axiom) they concluded that snakes are unrelated to mosasaurs, QED.

Actually, the molecular phylogeny result did look very surprising -
shocking! - at the time, to anyone who's studied squamate systematics and
palaeontology, because it puts Iguanian lizards in the same region of the
tree as anguimorphs and snakes, instead of right at the base (as in all
analyses since Camp 1923).  This has actually been backed up by additional
molecular evidence from multiple genes, so it seems to be one of those weird
cases of 'wholesale morphological atavism' (like the gavialine crocodyloids)
revealed by DNA.  The actual implication is that the common ancestor of all
anguimorphs was more like a varanid, and less like a gerrhosaur, than was
previously thought.

And it has no effect on the relationship of snakes with mosasauroids
supported by morphological evidence, which (at least until we get mosasaur
DNA) remains closer than that of snakes with extant varanids.
 
-----------------------------------------------
Dr John D. Scanlon
Palaeontologist, 
Riversleigh Fossil Centre, Outback at Isa
19 Marian Street / PO Box 1094
Mount Isa  QLD  4825
AUSTRALIA
Ph:   07 4749 1555
Fax: 07 4743 6296
Email: riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby


> -----Original Message-----
> From: Fulton Grant [mailto:blackphoenix@eastlink.ca]
> Sent: Saturday, April 22, 2006 9:34 AM
> To: dinosaur@usc.edu
> Subject: Re: New Limbed Cretaceous Snake
> 
> On 20-Apr-06, at 5:21 AM, Nick Pharris wrote:
> 
> > Quoting Danvarner@aol.com:
> >
> >> Large images:
> >>
> >> http://www.newscientist.com/article/dn9020-oldest-snake-fossil-
> >> shows-a-bit-of-
> >> leg.html
> >
> > <<Blair Hedges, an evolutionary biologist at Pennsylvania State
> > University, US, says: "In one fell swoop, this new fossil kind of
> > casts doubt on the aquatic hypothesis."
> >
> > His DNA sequencing studies suggest a terrestrial origin for snakes.
> > And he says that, looking at evolutionary history, it is difficult
> > to find examples of limb loss in an aquatic environment.>>
> 
> Can somebody please explain how DNA sequencing was done in relation
> to this fossil? Unless DNA was preserved with the specimen, which
> hasn't been mentioned AFAIK, DNA testing could only have been done
> with extant species - something that could've been don without even
> knowing this specimen existed.