The ackie (also known as ridgetail(ed) monitor, spiny-tailed monitor, or ackies dwarf monitor) is a diurnal, terrestrial monitor lizard native to the west, north, and center of northern Australia, including some islands off the northern coast. They prefer arid and seasonally dry habitats with lots of rocks, boulders, and spinifex grass, and often shelter in crevices between the rocks as well as burrows underneath them.                                                                              

Ackie monitors are long, slender monitors with a snakelike tongue, sharply tapered snout, somewhat rounded body, relatively short legs, and a whiplike tail. The body is typically red, brown, or black-brown with yellow, cream, or red spotting. The head typically features three pale stripes running from the face to the neck. The tail is long and covered in heavily keeled scales in a pattern of alternating light and dark rings, giving it a spiny appearance and function. The underside is typically pale and patternless.