The bird snakes (Pseustes & Spilotes) rearranged

The genus Pseustes Fitzinger, 1843 is composed of three known species, Pseustes poecilonotus, P. shropshirei and P. sulphureus. Pseuestes sulphureus may be the largest sized colubrid snake in the New World, although Drymarchon corias has a similar or possible greater size. But, both species may exceed 3 meters in total length. Pseustes has been classified as belonging to numerous other genera, over the years, including: Ahaetulla, Chironius, Coluber, Dipsas, Herpetodryas, Natrix, Phrynonax, Spilotes, Synchalinus, Thamnobius and Tropidodipsas. Pyron et al. (2013) found support that Pseustes sulphureus is the sister taxon to Spilotes pullatus, both members of the Colubrinae. However, the estimated phylogenetic position of this species was only based on a single 12S gene fragment as part of a large study. The study, used genes from 4161 species of squamates.  

In a forthcoming paper, Jaden et al. used multiple individuals of Pseustes across Central and South America and they analyzed the genus to infer the phylogenetic position of Pseustes within the Colubrinae, assess the relationship between Spilotes and Pseustes, and determine whether species of the genus Pseustes form a monophyletic group, infer phylogenetic relationships within Pseustes, and species-level diversity to resolve historical taxonomic debates. 

The authors examined four species from multiple specimens across their distribution and analysed one nuclear and two mitochondrial genes to determine the phylogenetic placement of the genus and infer relationships among Pseustes lineages. They found strong support for the paraphyly of Pseustes with respect to the monotypic genus Spilotes, both of which are nested within a clade of at least 23 other New World Colubrinae genera. 

The results produced a new view of the genera Psuestes and Spillotes. The authors resurrected the taxon P. polylepis for populations of P. poecilonotus from South America and moved P. sulphureus to the genus Spilotes which renders both genera monophyletic. Psuestes sulphureus is the type species of the genus Pseustes, and moving it to the genus Spilotes requires the allocation of the senior synonym Phrynonax be considered for the remaining Pseustes taxa.

Citation
Jadin RC., Burbrink FT, Rivas GA, Vitt LJ, Barrio‐Amorós CL, and; Guralnick RP. (2013). Finding arboreal snakes in an evolutionary tree: phylogenetic placement and systematic revision of the Neotropical birdsnakes. Journal of Zoological Systematics and Evolutionary Research. DOI: 10.1111/jzs.12055