The Spiny-tailed Monitor or Ridge-tailed Monitor (Varanus acanthurus) is a small species of monitor lizard. They are native to Northwestern Australia and even the eastern part of Queensland. They live in a variety of habitats from arid to tropical regions. Spiny-tailed Monitors are usually a reddish brown with yellow markings but color and pattern can vary with geographic origin. A distinctive feature is their thick spined tail - hence their common name. The Ridge-tail will scramble into loose rocks or boulders and use its tail to wedge itself in tight. The spikes give the tail good grip on the rocks, making extraction by other predators nearly impossible. In the species' home territory, the tail is often found discarded near Ridge-tail carcasses, indicating that predators of this species consider the tail inedible.
Their diet consists mainly of insects, mammals and lizards including other small monitors.