Family Viperidae include asps, moccasins, rattlesnakes, and true vipers and comprises about 260 species in four subfamilies, viz, Azemiopinae, Causinae, Crotalinae and Viperinae (McDiarmid et al, 1999).
Vipers of subfamily Viperinae are commonly called true vipers, Old world vipers or pitless vipers.
In another imperative study by Lenk et al., 2001, nucleotide sequences of mitochondrial cytochrome b (partial) and 16S rRNA genes, totaling 946 bp, have been used to reconstruct a molecular phylogeny of 42 species of the subfamily Viperinae representing 12 of the 13 recognized genera in order to further elucidate and clarify phylogenetic relationships in the viperine complex.
We analyzed phylogenetic relationships (1) of the lizard and snake families; (2) within eight families (Boidae, Colubridae, Elapidae, Typhlopidae, Viperidae, Anguidae, Iguanidae, and Scincidae); (3) within ten subfamilies (Alsophiinae, Colubrinae, Natricinae, and Psammophiinae for Colubridae;
Viperinae and Crotalinae for Viperidae; Diploglossinae and Gerrhonotinae for Anguidae; and Lygosominae and Scincinae for Scincidae); and (4) within seven genera (Elaphe and Natrix for Colubridae; Agkistrodon and Trimeresurus for Viperidae; Diploglossus and Elgeria for Anguidae; and Eumeces for Scincidae).