These unique snakes have caused great taxonomic confusion. Early classifications placed undue emphasis on the presence of erectile front fangs in burrowing asps. Due to this sole feature, for many years they were called mole vipers or burrowing adders and mistakenly were placed in the family Viperidae, even though they did not look like other vipers. It is now known that the fang erection mechanism of burrowing asps is unique and unlike that of true vipers.
Burrowing asps look very similar to and have similar lifestyles to other African burrowers, including the exotic-sounding purple-glossed snakes (Amblyodipsas), quill-snouted snakes (Xenocalamus), and centipede eaters (Aparallactus). They are now placed together, although confusion remains over the relationships and status of some genera within the family. Many have been combined into the snake eaters (Polemon), while at least one other genus (Elapotinus) is known from only a single specimen that may not even be African. The affinities of African burrowing snakes with other snakes also remain obscure. They share some intriguing similarities with primitive elapid snakes, e.g., the harlequin snakes (Homoroselaps) from South Africa, and may be close to the basal stock from which the important and venomous elapid snakes arose.
Two subfamilies are recognized. The Aparallactinae contains 11 genera, 25 species, of small- to medium-sized bur-rowers that are mainly back-fanged. The Atractaspidinae contains only a single genus (Atractaspis) with 17 species, distinguished by its unusual method of fang erection.
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