Living platynotan lizards are represented by two families: Helodermatidae, consisting of two species limited to south-western North America and north-western Central America; and Varanidae, with 54 species distributed throughout Africa, south-east Asia and Australia. Modern members of Platynota, universally adapted to a predaceous lifestyle and often specializing in relatively large vertebrate prey, include the largest living lizard and three species known to employ venom. Although relatively

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... pauperate, in terms of extant taxa, the 100 million year record of fossil Platynota reveals a widely distributed and morphologically diverse clade of predatory lizards. Several new taxa have been introduced in the past 30 years, many represented by complete skulls and skeletons yet the relationships among taxa found at the base of Platynota remain largely unresolved. Many basal platynotans have been placed within family Necrosauridae, the type genus of which is the most widely distributed and well represented fossil platynotan. As currently constituted the Necrosauridae is presumed to be paraphyletic and lacks a clear and concise diagnosis as does the type genus Necrosaurus. Amended diagnoses are provided for Necrosaurus and the Necrosauridae and the membership of taxa previously placed within Necrosauridae is examined. Phylogenetic analysis of fossil platynotans recovers a monophyletic Necrosauridae in a sister-group relationship to a clade containing modern varanids.