Snake Evolution Revisted

["Jaime A. Headden" <qilongia@yahoo.com>]

  This is a general-interest (read: non-dinosaur) publication.


  Wiens, J.J. & Slingluff, J.L. 2001. How lizards turn into snakes: A 
phylogenetic analysis of
body-form evolution in anguid lizards. _Evolution_ 55 (11): 2303?2318.
abstract reads:

  "One of the most striking morphological transformations in vertebrate 
evolution is the
transition from a lizardlike body form to an elongate, limbless (snakelike) 
body form. Despite its
dramatic nature, this transition has occurred repeatedly among closely related 
species (especially
in squamate reptiles), making it an excellent system for studying 
macroevolutionary
transformations in    body plan. In this paper, we examine the evolution of 
body form in the
lizard family Anguidae, a clade in which multiple independent losses of limbs 
have occurred. We
combine a molecular phylogeny for 27 species, our morphometric data, and 
phylogenetic comparative
methods to provide the first statistical phylogenetic tests of several 
long-standing hypotheses
for the evolution of snakelike body form. Our results confirm the hypothesized 
relationships
between body elongation and limb reduction and between limb reduction and digit 
reduction.
However, we find no support for the hypothesized sequence going from body 
elongation to limb
reduction to digit loss, and we show that a burrowing lifestyle is not a 
necessary correlate of
limb loss. We also show that similar degrees of overall body elongation are 
achieved in two
different ways in anguids, that these different modes of elongation are 
associated with different
habitat preferences, and that this dichotomy in body plan and ecology is 
widespread in
limb-reduced squamates. Finally, a recent developmental study has proposed that 
the transition
from lizardlike to snakelike body form involves changes in the expression 
domains of midbody Hox
genes, changes that would link elongation and limb loss and might cause sudden 
transformations in
body form. Our results reject this developmental model and suggest that this 
transition involves
gradual changes occurring over relatively long time scales."


=====
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.

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