Varanidae

The Varanidae are a family of lizards of the superfamily Varanoidea. The family, a group of carnivorous and frugivorous lizards, includes the Megalania (the largest known lizard), the Komodo dragon (the largest living lizard), and the crocodile monitor. The Varanidae contain the living genus Varanus and a number of extinct taxa. Their closest living relatives are the anguid and helodermatid lizards.

It was defined by Estes, de Queiroz and Gauthier (1988) as the clade containing the most recent common ancestor of Lanthanotus and Varanus and all of its descendants. A similar definition was formulated by Conrad (2008), who defined Varanidae as the clade containing Varanus varius, Lanthanotus borneensis, and all descendants of their last common ancestor. Using one of these definitions leads to the inclusion of the earless monitor lizard (Lanthanotus borneensis) in the family Varanidae. Lee (1997) created a different definition of Varanidae, defining it as the clade containing Varanus and all taxa more closely related to Varanus than to Lanthanotus; this definition explicitly excludes the earless monitor lizard from Varanidae. Whether Lanthanotus borneensis is included in or excluded from Varanidae depends on the author: for example, Vidal et al. (2012) classify the earless monitor lizard as a member of a separate family Lanthanotidae, while Gauthier et al. (2012) classify it as a member of Varanidae.

Biology
Monitor lizards are reputed to be among the most intelligent lizards. Most species forage widely and have large home ranges, and many have high stamina. Although most species are carnivorous, three arboreal species in the Philippines (Varanus olivaceus, Varanus mabitang, and Varanus bitatawa) are primarily frugivores. Among species of living varanids, the limbs show positive allometry, being larger in larger-bodied species, although the feet become smaller as compared with the lengths of the other limb segments.

Uniquely among squamates, varanids possess unidirectional pulmonary airflow, including airsacs akin to those of birds.