Varanus (Hapturosaurus)

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Varanus (Hapturosaurus) are slender, arboreal lizards known as tree monitors. They live in tropical forests of Indonesia and Papua New Guinea and belong to the family Varanidae. In 2016, scientists created the subgenus Hapturosaurus to group all species that belong to the Varanus prasinus complex, with the green tree monitor (Varanus prasinus) as the type species.

The subgenus includes nine species: Varanus beccarii, V. boehmei, V. bogerti, V. keithhornei, V. kordensis, V. macraei, V. prasinus, V. reisingeri, and V. telenesetes. The name Hapturosaurus comes from Greek words meaning “to grasp,” “tail,” and “lizard,” highlighting their long, prehensile tails. All species are highly arboreal.

The green tree monitor has the broadest distribution, while most other species are island-endemic to parts of Indonesia or Papua New Guinea. Their ancestors spread through the Indo-Pacific during the Pleistocene when lower sea levels created land bridges between New Guinea and Australia. There have been occasional reports of green tree monitors on Cape York Peninsula in Australia, which would put them in contact with the canopy goanna.

In behavior and biology, tree monitors are very intelligent and show advanced problem-solving abilities. In captivity they can exhibit play-like behaviors, such as destroying plant leaves with their teeth and claws. They are mainly insectivorous, eating insects and other small invertebrates, and occasionally small vertebrates or bird eggs. Hatchlings may not eat for about two weeks after hatching, and keepers sometimes need to assist feeding during that period.

A notable feature is their forelimbs: they have long, slender arms with strong claws and adhesive soles, which they use to hook prey from crevices when their jaws can’t reach. This adaptation helps them exploit a wide range of hunting niches.

Like other monitor lizards, tree monitors have venom glands in their lower jaws. Their venom is an anticoagulant that disrupts blood clotting by breaking down fibrinogen and inhibiting platelet aggregation, and it can cause a drop in blood pressure. Their venoms are especially potent in fibrinogenolysis, which helps subdue agile prey in trees. Bites can bleed more than expected because of the venom’s effects.