The sand monitor, Varanus gouldii, ranges throughout much of northern and western Australia and southern New Guinea. It is one of the largest Australian monitors, and is sometimes known as the "racehorse monitor" because it is capable of extreme speed, often running bipedally. The subspecies featured here, V. g. horni (the Argus monitor), lives in southern New Guinea.
Varanus includes over 45 living species and subspecies, among them the formidable Komodo dragon, V. komodoensis. Half of the living species occur in Australia, with the rest in Africa and Asia. Among extant lizards, varanids are most closely related to Lanthanotus borneensis (the earless "monitor") and Gila monsters (Heloderma), and together these lineages comprise Varanoidea. Varanoidea is thought to have evolved in Asia by at least 90 million years ago, whereas the oldest representatives of Varanus date to 25 million years ago.
The varanid skull is distinguished by a number of features, including an elongate fork-shaped premaxilla, fifteen scleral ossicles, and contact of the descending processes of the frontals below the olfactory tracts. The impressive predatory capability of monitor lizards derives in part from the highly developed and mobile hyoid apparatus. Much of the hyoid is discernible in the CT imagery because it is ossified or highly calcified (rather than cartilaginous); this degree of hyoid mineralization is unusual among lizards.
Bennett, D. 1998. Monitor lizards: natural history, biology and husbandry. Edition Chimaira, Frankfurt am Main.
Estes, R., K. de Queiroz, and J. Gauthier. 1988. Phylogenetic relationships within Squamata, pp. 119-281. In R. Estes and G. Pregill (eds.), Phylogenetic Relationships of the Lizard Families: Essays Commemorating Charles L. Camp. Stanford University Press, Stanford, California.
Maisano, J. A. 2000. Postnatal skeletal development in squamates: Its relationship to life history and potential phylogenetic informativeness. Unpublished PhD Dissertation, Yale University, 1227 pp.
Pregill, G. K., Gauthier, J. A., and H. W. Greene. 1986. The evolution of helodermatid squamates, with description of a new taxon and an overview of Varanoidea. Transactions of the San Diego Natural History Museum 21:167-202.
Sprackland, R. G. 1992. Giant Lizards. T. F. H. Publications, Neptune, New Jersey.
Varanus gouldii on the Animal Diversity Web (The University of Michigan Museum of Zoology)
Learn more about varanid evolution on Dr. Eric Pianka's page
Varanus reference lists of Dr. Daniel Bennett and Dr. Graham Thompson