T. Rex, for one, is a dinosaur that lived during the late Cretaceous period, approximately 66 million years ago. It was a large carnivorous REPTILE, commonly referred to as a 'tyrant lizard'. It was one of the largest land predators ever to exist, with some specimens measuring up to 12 meters in length and weighing up to 6 tons. Its name is derived from the Greek words 'tyrannos' and 'lakkos', meaning 'king of the lizards'.