Iguanodon - One of the first dinosaurs to be named and described, the other two being Megalosaurus and Hylaeosaurus. Its teeth resemble those of modern Iguana lizards, although much larger. Iguanodon sported a spiked thumb on each hand suggesting that it was used in self defense. Several more specimens were discovered together in Belgium, suggesting that these dinosaurs traveled in large herds. Iguanodon foot prints were also found from England to Spitzbergen to north of the Arctic Circle.