Two views of squamate systematics based on morphology
Position of Iguania as basal split between Iguanians and other Squamates (Scleroglossans). This is
in both of them.
Then, as go through scleroglossans
Estes: Geckoes at base of scleroglossans
Then, Scincomorphs and Anguimorphs
Lee: Again Geckoes at bottom of Scleroglossa but joined by some groups not seen in Estes tree.
Again, anguimorphs and scincomorphs in same rough area, but scincomorphs are not a clade in
Limblessness has evolved many times. Problem with placing these limbless taxa is that it is
possible that limblessness can mislead morphological analysis – maybe put all of them together,
but this is misleading because loss of limbs recurs independently. Maybe just exclude limbs! If truly
limbless clades come together, should see other aspects of morphology come together. But the
problem is that with limblessness, there are other things that come with it.
So, Estes just place them deep in scleroglossan tree
Lee threw out limbs and a lot of other characters and found snakes where you would expect, near
Varanids, but amphisbaenians and dibamids were put together, close to gekkoes.
But, tree from DNA was very different from tree by morphology.
Gekkoes were almost at the very bottom of the tree. Second, Iguanians are monophyletic, but not
at bottom of tree, but nested in the middle of lizard phylogeny.
Angiumorphs are a group, excepted that iguanians are right in the middle of anguimorphs, which
had never been suggested
Limbless forms not at all closely related – snakes more or less in expected position, in middle of
anguimorphs, but not near Varanids, while Dibamids are at the very bottom of lizard phylogeny.
Amphisbaenians are sister taxa to Lacertids – completely unexpected.
Scincomorphs are kind of all over the tree.
In fact, not a single morphological factor that supports dna placement of iguanids. In fact, estimated
60 trait reversals in iguanians.
If look at components of venom some hypotheisis that vemins it the natural, basal, ancestral state
for this clade
Evolutionary trends in lizards
Evolution of limblessness
22 evolutions of limblessness
Many of the species are either burrowers or live in grassy areas. Burrowers tend to have short tails,
but grasslands usually have longer tails. Snakes are more diverse.
Why heterogeneity? Evolves in some cases but not others
Liolaemus has evolved herbivory 18 times within Iguanidae. No herbivorous gekkoes, no snakes, 8
More than 100 times
Head ornaments: Igunian lizards
Dorsal spines (Iguanians). Essentially nothing in Scleroglossans, with one exception: there are
some snakes that have things on heads! Horns, eyelash viper, etc.
Territory: any area defended against conspecifics