If you were tempted to think ‘some kind of dinosaur’, then think again – dinosaurs were similar to reptiles but weren’t lizards. The answer is varanus priscus, or megalania, a terrestrial lizard native to Australia that became extinct over 40,000 years ago. Although most experts agree megalania was the biggest ever, opinion is divided on just how big it was, with estimates varying between 4.5-7 metres (14.7-23 feet).
This is because no complete skeletons have been found, although fossil fragments do suggest megalania was heavily built with a mouthful of sharp, serrated teeth. The world’s largest living lizard is a distant relative of megalania, the Komodo dragon, which is a kind of monitor lizard.