Stegosaurus means "covered lizard" in Greek. This dinosaur had a double row of protective plates covering its back and tail. In addition to acting as a protective covering, these plates may have operated as a sort of cooling device -- wind flowing between the plates would have helped lower the body temperature of a Stegosaurus on hot days. The Stegosaurus is known to have grown as tall as 12 meters (40 feet) and weighed as much as 5 tons.
The Argentinosaurus, an herbivorous sauropod and quite possibly the largest animal ever to walk the earth, is believed to have reached lengths of up to 45 meters (150 feet) and weighed as much as 110 tons! Only fragmentary remains have been discovered, but using their knowledge of related dinosaurs, scientists have been able to estimate the size of these specimens of Argentinosaurus.
An average Tyrannosaurus Rex had arms that were only about 1 meter (3 feet) long. However, with a 1 1/2 meter jaw filled with 50 to 60 nine-inch serrated teeth, the T-Rex may not have needed to use his hands much! Bite marks on other fossils suggest that he could bite through solid bone! And if he broke a few teeth here and there, no big deal -- new ones continually grew in to replace those that he lost. Standing up to 15 meters high and weighing more than 5 tons, Tyrannosaurus Rex was massive -- but he was not the largest carnivorous dinosaur. Giganotosaurus was even bigger.
Dinosaurs first appeared during the Triassic period. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research, the current scientific consensus places their origin between 231 and 243 million years ago.
Charles R. Knight (1874-1953) was an American artist best known for his influential paintings of dinosaurs and other prehistoric animals. Knight's most famous work depicts the classic confrontation between the horned dinosaur Triceratops and its deadly adversary Tyrannosaurus rex.