Electronic Supplement 4
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Organisms
Diversity & Evolution 5 (2005) Electronic Supplement 4 |
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Michael S. Y. Lee:
Squamate phylogeny, taxon sampling, and data
congruence.
print version: Org. Divers. Evol. 5(1): 25-45. 2005 (full
article)
electr. suppl.:
Part 1. List of morphological characters.
pdf-format, 196 KB
Part 2. NEXUS-file for
phylogenetic analysis. nxs-format, 17 KB
Abstract:
To investigate the affinities of snakes,
amphisbaenians and dibamids, the phylogenetic relationships among the major
lineages ('families') of extinct and extant squamates are assessed through a
combined analysis of 248 osteological, 133 soft-anatomical, and 18 ecological
traits. The osteological data set represents a revision of previous data,
taking into account recent criticism; the ecological data set is new. In
addition, potentially critical fossil taxa (polyglyphanodontids and
macrocephalosaurs) are included for the first time. The osteological and
soft-anatomical data sets each place snakes within anguimorphs and dibamids,
and amphisbaenians near gekkotans, with the putative primitive fossil
amphisbaenian Sineoamphisbaena grouping with macrocephalosaurs, and
polyglyphanodontids as the sister group to scleroglossans. All three data sets
are congruent, and these results are reinforced by combined analyses. In these,
as in the osteological analyses, snakes are nested within marine lizards.
However, exclusion of fossil taxa from the osteological data set results in a
'limbless clade' consisting of snakes, amphisbaenians, and dibamids, and
introduces significant conflict between osteology and soft anatomy. Also,
deletion tests and character weighting reveal that the signal in the reduced
osteological data set is internally contradictory. These results increase
confidence in the arrangement supported by the all-taxon osteological, the
soft-anatomical, and the combined data, and suggest that exclusion of fossils
confounds the signal in the osteological data set. Finally, the morphological
data supports the nesting of snakes within marine lizards, and thus a marine
origin of snakes. This result still holds when relationships between living
forms are constrained to the topology suggested by molecular sequences: if
marine lizards are allowed to 'float' within this molecular framework, they
form the stem group to snakes, and do not group with varanids as previously
suggested.
Key words: Squamata; Snakes; Amphisbaenians; Dibamids; Partitioned branch support; Character congruence
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