According to Nicholas Vidal (2002), "Only one genus, the genus Atractaspis, displays a frontfanged venom system, but it is not homologous to the solenoglyph apparatus of the vipers.[27,28]"



Additionally, Harry Greene (1997:43) notes that "Most snakes coil and strike in a roughly horizontal plane, but stiletto snakes (Atractaspis) and some elapids fling their heads forward, downward, or backward to bite."



Heise et al.'s (1995) mtDNA data shows that Atractaspis is closely related to Bungarus and it lies within the Elapidae.



Three lines of evidence (behavior, phylogenetics and morphology) thus suggest that Atractaspis is an elapid, not a colubrid or viperid. Other elapids are known to have slightly movable front fangs, e.g. Acanthophis and Dendroaspis.



Reference:

Greene, H.W. 1997. Snakes. The Evolution of Mystery in Nature. Univ. California Press.



Vidal, Nicolas 2002. Colubroid Systematics: Evidence for an Early Appearance of the Venom Apparatus Followed by Extensive Evolutionary Tinkering. J. Toxicol.—Toxin Reviews, 21(1&2), 21–41

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