Boid taxonomy revisited


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 Charinaand 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.
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.
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. 10.1016/j.ympev.2013.11.011.

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