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varanids, etc. fwd from J. Headden



Due to tech difficultities Jaime requested I forward this note to the
DML.

dp




Subject:
         Re: looking for a primitive varanid
    Date:
         Thu, 20 Jan 2005 16:47:54 -0800 (PST)
   From:
         "Jaime A. Headden" <qilongia@yahoo.com>
     To:
         david peters <davidrpeters@earthlink.net>




David Peters (davidrpeters@earthlink.net) wrote:

<Just wondering what one looks like.>

  The other varanoids include *Lanthanotus* (earless monitor) and the
helodermatids (including the Gila monster, beaded lizard, etc.,
*Heloderma,* and allies). Outside of this, they remain relatively
similar
with less specialized otic regions and coronoids, as well as the palate.

There is nothing particularly "different" about their general
appearance.
Anguids and xenosaurids represent outgroups, including the Chinese water

dragon, and these should provide further consideration of the
"primitive"
varanid.

<Mosasaurs and their predecessors would seem to be derived from
Varanus-types, because they have legs, but Varanus apparently has fewer
and looser bone connections in the skull.>

  Feeding in mosasauroids has evolved from the clidastine towards the
mosasaurine morphotypes into an expanding jaw with a rigid neurocranium
and loss of the relatively weak intracranial kinetic joints. The
prokinetic joint remained largely present but weak in mosasauroids. Work

by Caldwell and Lee alaborates. References include:

  Caldwell, M.W. 1999. Squamate phylogeny and the relationships of
snakes
    and mosasauroids. _Zoological Journal of the Linnean Society_
    125:115-147.

  Lee, M.S.Y. 1997. The phylogeny of varanoid lizards and the affinities

of
    snakes. _Philosophical Transactions of the Royal Society of London_
B
    352:53-91.

  Closer of sutures may have been neccessary to larger vertebrate or
invertebrate feeding (shellfish), so mechanical advantage is in loss of
intraosteal kinetic joints in the cranium and a more mobile, flexible
jaw
gape.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making
leaps in the face of adversity, that a simple skip is so hard to do.  We
should all learn to walk soft, walk small, see the world around us
rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)



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