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Re: legless lizards?



Jason wrote-

> Am I reading that right? Did they completely throw out
> the Iguania-Scleroglossa split? Furthermore, they nest
> Iguania well inside Scleroglossa.

Yup.

> According to the above cladogram, Townsend et al, seem
> to suggest that iguanian archaic traits, are only
> superficial. This would mean that they re-evolved a
> fleshy tongue (which would have been long since
> decoupled from food acquisition; based off the close
> relationship to teiids), then re-evolved the upper
> temporal arch, and re-evolved a more robust skull to
> go with it. 

They write-
"Our results suggest reinterpretation of studies that
have used comparative methodology to contrast Scleroglossa
and Iguania. For example, Schwenk (1993)
found a fundamental difference in tongue morphology
and prey-prehension technique between iguanian (lingual
prehension) and scleroglossan (jaw prehension)
lizards. Schwenk (1986) reported that the tongue of
Sphenodon (a lingual feeder) shares many features with
iguanid lizards, including muscle-fiber architecture and
hyobranchial-foretongue coupling. Based on these similarities,
along with independent evidence for a basal dichotomy
within squamates between Iguania and Scleroglossa
(Estes et al., 1988), Schwenk (1986) concluded
that Sphenodon and iguanians exhibit the ancestral squamate
(and lepidosaurian) condition. This inference of the
ancestral condition is problematic, however, because jaw
prehension is widespread in the closest outgroups to
lepidosaurs (birds, turtles, and crocodilians). Schwenk
(1989) cites examples of lingual prehension in some of
these groups as evidence that it is the ancestral state;
however, given the difficulty in comparing the highly
modified feeding apparatus between these distantly related
groups (Schwenk, 1988), this conclusion may be
unwarranted.
......
Under our phylogenetic hypothesis, iguanians and
Sphenodon (or some possibly distant ancestor to Sphenodon)
are inferred to have acquired lingual preyprehension
techniques independently (Fig. 9). Because
food prehension techniques, tongue musculature,
and chemosensory ability are unknown for rhynchocephalians
other than Sphenodon, this scenario is only
slightly less parsimonious than the traditional view. Although
similarities in muscle fiber and connective-tissue
architecture between Sphenodon and iguanians may be
explained most parsimoniously by symplesiomorphy
(Schwenk, 1986), if lepidosaurian feeding systems truly
are highly integrated and constrained, tongue morphology
could evolve to be markedly similar in unrelated
groups adopting the same feeding mode. Indeed, the apparent
lability of feeding mode and tongue morphology
is exemplified in the recovery (with each of the three
gene regions) of an iguanian-anguimorph-snake clade, a
group that represents the extremes of these traits within
squamates."

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