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a little more from the paper....

Among extant reptiles only two lineages are known to have evolved venom delivery systems, the advanced snakes and helodermatid lizards (Gila Monster and Beaded Lizard)1. Evolution of the venom system is thought to underlie the impressive radiation of the advanced snakes (2,500 of 3,000 snake species)2–5. In contrast, the lizard venom system is thought to be restricted to just two species and to have evolved independently from the snake venom system1. Here we report the presence of venom toxins in two additional lizard lineages (Monitor Lizards and Iguania) and show that all lineages possessing toxin-secreting oral glands form a clade, demonstrating a single early origin of the venom system in lizards and snakes. Construction of gland complementary-DNA libraries and phylogenetic analysis of transcripts revealed that nine toxin types are shared between lizards and snakes. Toxinological analyses of venom components from the Lace Monitor Varanus varius showed potent effects on blood pressure and clotting ability, bioactivities associated with a rapid loss of consciousness and extensive bleeding in prey. The iguanian lizard Pogona barbata retains characteristics of the ancestral venom system, namely serial, lobular non-compound venom-secreting glands on both the upper and lower jaws, whereas the advanced snakes and anguimorph lizards (including Monitor Lizards, Gila Monster and Beaded Lizard) have more derived venom systems characterized by the loss of the mandibular (lower) or maxillary (upper) glands. Demonstration that the snakes, iguanians and anguimorphs form a single clade provides overwhelming support for a single, early origin of the venom system in lizards and snakes. These results provide new insights into the evolution of the venom system in squamate reptiles and open new avenues for biomedical research and drug design using hitherto unexplored venom proteins.

Cool. Does this mean that Gila monsters and Mexican beaded lizards are basal forms? In my beloved old Funk and Walgalls Wildlife Encyclopedia (still have 'em; everyone should!), the section on the hog-nosed snake suggested that the snake was "on its way" to becoming venomous in a few generations, due to certain features it shared with venomous snakes, notably a saliva that is toxic to the frogs and toads it preys on. It now seems more likely to me, according to this article, that the hog-nose is instead related to those first species which were on the way out from being venomous, but that it retained certain poison-producing glands which became specifically toxic for a snake with a very specialized diet, and that its threat display may be a behavioral hanger-on from its venomous days, that is still useful today.