Four New World genera of dwarf boas (Exiliboa, Trachyboa, Tropidophis, and Ungaliophis)
have been placed by many systematists in a single group (traditionally called Tropidophiidae).
However, the monophyly of this group has been questioned in several studies. Moreover,
the overall relationships among basal snake lineages, including the placement of the
dwarf boas, are poorly understood. We obtained mtDNA sequence data for 12S, 16S, and
intervening tRNA-val genes from 23 species of snakes representing most major snake
lineages, including all four genera of New World dwarf boas. We then examined the
phylogenetic position of these species by estimating the phylogeny of the basal snakes.
Our phylogenetic analysis suggests that New World dwarf boas are not monophyletic.
Instead, we find Exiliboa and Ungaliophis to be most closely related to sand boas
(Erycinae), boas (Boinae), and advanced snakes (Caenophidea), whereas Tropidophis
and Trachyboa form an independent clade that separated relatively early in snake radiation.
Our estimate of snake phylogeny differs significantly in other ways from some previous
estimates of snake phylogeny. For instance, pythons do not cluster with boas and sand
boas, but instead show a strong relationship with Loxocemus and Xenopeltis. Additionally,
uropeltids cluster strongly with Cylindrophis, and together are embedded in what has
previously been considered the macrostomatan radiation. These relationships are supported
by both bootstrapping (parametric and nonparametric approaches) and Bayesian analysis,
although Bayesian support values are consistently higher than those obtained from
nonparametric bootstrapping. Simulations show that Bayesian support values represent
much better estimates of phylogenetic accuracy than do nonparametric bootstrap support
values, at least under the conditions of our study.
Copyright 2002 Elsevier Science (USA)