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Re: legless lizards?



David Peters wrote-

> I've read a few papers recently and it seems that Amphisbaena ("legless"
> lizards) are not well placed. I see alot of big question marks in family
> trees. Force fits.
>
> Are we even sure that they are lizards?

Townsend et al. (2004) found good evidence they are the sister group to
Lacertidae (100% bootstrap, decay index of 31), and both of these are sister
to Teioidea (76% bootstrap, decay index of 10).  All three groups make up
the Lacertiformes.  They write regarding Amphisbaenia + Lacertidae-

"This latter relationship may be supported by a structural character as
well. Gallotia (a lacertid) has a seven-codon deletion at c-mos positions
220 to 240, and all sampled amphisbaenians share  an overlapping eight-codon
deletion at positions 217 to 240, suggesting that the original deletion was
simply extended by one codon in amphisbaenians. Harris et al. (1999)
reported a seven-codon deletion in this general region for two gekkonines.
Although the alignment in this area is not completely unambiguous,
alignments made with Clustal X (Thompson et al., 1997) at a variety of gap
penalties (see Materials and Methods) suggest that the lacertid and
gekkonine deletions do not involve the same codon positions. Furthermore,
forcing the gekkonine and lacertid deletions to coincide requires two
separate, smaller amphisbaenian deletions instead of the one found at all
Clustal gap-penalty settings used."

Townsend, Larson, Louis and Macy, 2004. Molecular Phylogenetics of Squamata:
The Position of Snakes, Amphisbaenians, and Dibamids, and the Root of the
Squamate Tree. Syst. Biol. 53(5):735-757.

In case any of you are wondering, the suggested squamate phylogeny in this
paper is-
|--Dibamidae
|--Gekkonidae
`--+--+--Scincidae
   |  `--+--Xantusiidae
   |     `--Cordylidae
   `--+--+--Iguanidae
      |  `--+--Agamidae
      |     `--Chameleonidae
      |--+--+--Teiidae
      |  |  `--Gymnophthalmidae
      |  `--+--Lacertidae
      |     `--Amphisbaenia
      |--Serpentes
      `--+--+--Varanidae
         |  `--Shinisaurus
         `--+--Anguidae
            |--Helodermatidae
            `--Xenosaurus
All nodes were supported by >95% posterior probability and bootstrap in the
analysis of nuclear genes RAG-1 and c-mos

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html