They look like dragons. Armed with sharp teeth, tearing claws and a whip-like tail, these fearsome creatures are not only powerful, they're also smart. Top predators with intelligence, who learn as they hunt, and are calculating when tracking prey. Sounds like these cunning hunters should be a big-brained mammal, but these creatures are reptiles, members of a family that evolved when the dinosaurs roamed the planet. They are the largest lizards still walking on Earth: monitor lizards. Ranging in size from the 3-metre long Komodo Dragon to the 20-cm short Pygmy Monitor, this huge scale range within a single genus - roughly the difference in body mass between an elephant and a mouse - is unmatched by any other group of terrestrial animals. Like all reptiles, monitor lizards are cold-blooded, lay eggs and shed their scaly skins. But that's where the similarities end. They have an intelligence you'd expect from mammals, and way beyond that of other reptiles. Find out exactly how bright they really are.