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| Two phylogenetic trees from recent papers that included boid snakes. |
In
a new paper Pyron et al. (2014)
discuss and alter the taxonomy of boid snakes. The family Boidae previously comprised
five subfamilies: Sanziniinae, Charininae, Erycinae, Candoiinae, and Boinae.
These subfamilies are distinct both morphologically and biogeographically, with
Sanziniinae being restricted to Madagascar; Charininae found in North and Central America (although Ungaliophis panamensis also inhabits a
small portion of western Colombia); Erycinae ranges from North Africa, Europe, the Middle
East, and South and Central Asia; Candoiinae occurs in Oceania; and Boinae is
restricted to the Neotropics. However, Boidae was rendered paraphyletic by
recent molecular phylogenetic analyses by the African family Calabariidae (Calabaria), which forms the sister-group
to Sanziniinae (Reynolds et al. 2014),
or all boids to the exclusion of Sanziniinae (Pyron et al. 2013). Therefore, current taxonomy does not reflect
monophyletic groups in the analyses sampling the most characters and taxa.
Thus, the authors are presented with a number of biogeographically distinct
subfamilies, all of which are strongly supported as monophyletic in essentially
all recent molecular phylogenetic analyses and by available morphological data.
Relationships among these subfamilies are variable, and in some analyses another
family-level taxon renders the family paraphyletic. They suggest that the most
straightforward action is to change the rank of the boid subfamilies to
families, for which family-series names are already available under the
Principle of Coordination. This resolves all nomenclatural problems revealed by
phylogenetic analyses, as all groups are monophyletic, and relationships among
them do not then affect their rank.
Calabaridae
contains one genus with one species, Calabaria
reinhardtii from West Africa. Calabariids lack of palatine teeth, have premaxillary
teeth, the supraorbital bone lacks a dorsal lobe, enlarged head shields, and
oviparous reproduction. Calabaria
reinhardtii was long considered a python, and it was synonymized with the
North American Charina. However molecular
phylogenetic analyses clearly show booid affinities, as well as distinctiveness
from all other booid genera.
Sanziniidae
contains two genera restricted to Madagascar, Acrantophis and Sanzinia.
Sanziniids can be distinguished by their mineralized internarial septum with a
small fenestra, postorbital and frontal broadly separated by the parietal,
distal border of the optic foramen formed mostly by the parietal with anterior
margin formed by the frontal, posterior trunk intercostal arteries supply one
body segment each, hemipenis with longitudinal flounce, and sulcus terminating
below the tips of the arms, as well as other traits. Acrantophis and Sanzinia are
more closely related to S. madagascariensis than Calabaria reinhardtii. Previously this
group include the Mauritian taxa (the Round Island boas) Bolyeria and Casarea but
they are only distantly related and not considered members of the clade under discussion.
Charinidae
contains four genera in two subfamilies Charina
and Lichanura (Chariniinae) and Exiliboa and Ungaliophis (Ungaliophiinae), Charinids can be distinguished by a
distinct lateral muscular bundle (M.) in the jaw known as the adductor
mandibulae externus medialis pars anterior, loss of the left lung, as well as
other traits. Distribution is in North and Central America, including southern
Canada, the western United States and northwestern Mexico for Charininae, and
southwestern Mexico, Central America, and extreme northwestern South America
for Ungaliophiinae. This group has had a turbulent taxonomic history, but
recent molecular results are unambiguous in supporting the monophyly of this
group and uniting it with Booidea.
Erycidae
contains the single genus Eryx. Erycids
can be distinguished by the following combination of characters: transverse
process of the premaxilla long, internarial septum of the premaxilla absent,
vomerine process of the premaxilla long and narrow, anterior one-third to
one-half of the ventral lamina of the nasal decreases anteriorly or is absent, dorsal
head scales small and usually asymmetrically arranged, and 34 diploid
chromosomes, as well as other traits. Distribution ranges from Southeastern
Europe, northern Africa, Middle East, and southwestern Asia. Fossil remains
from North America have been assigned to this clade, it will be interesting to
see of Erycids were actually present in North America or, the remains belong to
another clade – which seems more probable.
Candoiidae
contains one genus, Candoia. Candoiids can be distinguished by the
following combination of characters: low distinct posterior hypapophyseal keel
on trunk vertebrae, lack of labial pits, lack of paired common carotid
arteries, flattened rostrum leading to an angular snout, dorsal margin of the
transverse process of the premaxilla adjacent to the nasal process forms a thin
high wall noticeably curved posteriorly, body scales keeled, hemipenis with
well-defined longitudinal flounce and sulcus terminating below the tips of the
arms, as well as other traits. Distribution. Candoiidae is restricted to the
Pacific islands of New Guinea and Melanesia, and the eastern Indonesian
archipelago. One species occurs in the Palauan archipelago of western
Micronesia. Divergence-time estimates support a vicariant origin of Candoiidae
with intermediate extinction from other Gondwanan landmasses, as early
divergences in Boidae pre-date the final breakup of Gondwana.
Family
Boidae contains five genera, Boa, Chilabothrus, Corallus, Epicrates, Eunectes. Boids can be distinguished by
the following combination of characters: internarial septum with large
fenestra, anterior margin of the ventral lamina of the nasal indented in
lateral view, anterolateral margin of horizontal lamina of nasal noticeably
indented viewed dorsally, horizontal lamina of the nasal does not overlap
dorsal surface of frontal, shallow labial pits and other traits. Distribution
is restricted to the New World tropics, from northern Mexico to Argentina, and
the West Indies.
Citations
Pyron, R. A., Reynolds, R. G., & Burbrink, F.
T. (2014). A Taxonomic Revision of Boas (Serpentes: Boidae). Zootaxa, 3846(2), 249-260.
Pyron,
R.A., Burbrink, F.T. & Wiens, J.J. (2013) A phylogeny and revised
classification of Squamata, including 4161 species of lizards and snakes. BMC
Evolutionary Biology, 13, 93. http://dx.doi.org/10.1186/1471-2148-13-93.
Reynolds,
R.G., Niemiler, M.L. & Revell, L.J. (2014) Toward a Tree-of-Life for the
boas and pythons: multi locus species-level phylogeny with unprecedented taxon
sampling. Molecular Phylogenetics and Evolution, 71, 201–213.
http://dx.doi.org/ 10.1016/j.ympev.2013.11.011.