Megalania was a giant lizard, between 4.5 m (15 ft) and 7.9 m (26 ft) (depending on which size estimate you trust) in length, with a weight of between 331 kg (730 lb) and 600 kg (1,300 lb). Its name means "ancient giant roamer", not "ancient giant butcher" as some mistaken descriptions assert. Megalania lived in Australia during the Pleistocene, between about 1.6 million and 40,000 years ago. Megalania was the largest lizard that ever lived, and because of its size, is sometimes referred to as the "Dragon of the Australian Outback." Megalania is also known as the giant goanna, and it was related to the goanna lizards of today, including the largest extant lizard, the Komodo Dragon, though it is more closely related to the Perentie, Australia's largest lizard today.

巨蜥的嘴里长满了锯齿状的锋利牙齿，像弯刀一样。 从它的体型来看，它可能吃中大型动物，特别是像Diprotodon、大袋鼠和大袋鼠这样的巨型有袋动物。 由于没有巨型动物作为食物，像巨蜥这样的蜥蜴在今天是不可能进化的。 从巨蜥在4万年前灭绝，大约在人类到达非洲大陆时，看来人类很可能因为夺走了它的食物来源-大型动物而导致其灭亡。

作为一只巨蜥，Megalania可能是聪明的爬行动物。 所有的巨蜥都有高于其他蜥蜴的新陈代谢率，以及一些帮助它们猎取活的猎物的感官适应性。 活的巨蜥可以用后腿站立并观察它们的环境，这一特性使它们得名。 作为最聪明的蜥蜴，其他巨蜥已被证明能够数到6（通过在圣地亚哥动物园用蜗牛进行仔细的喂养研究），用诱饵欺骗鳄鱼来偷它们的蛋，在觅食时合作，甚至有独特的性格。

有时会有关于活体巨蜥的报告，尽管这些报告几乎可以肯定是假的，因为这些报告是在科学杂志上描述该物种后才开始出现的。