The word dinosaur was coined by Richard Owen in 1841, deinos (terrible) + sauros (lizard) which describe various extinct reptiles of the orders Saurischia and Ornithischia that flourished during the Mesozoic Era. Dinosaurs were carnivorous or herbivorous, dwelled mostly on land, and varied from the size of a small dog to the largest land animals that ever lived. The brontosaurus was a large herbivorous dinosaur, perhaps the most familiar of the dinosaurs. The scientific name has recently been changed to Apatosaurus, but Brontosaurus is still used popularly. The word is from the Greek, meaning "thunder lizard." It was one of the largest land animals that ever existed, with an average length of 75 ft and a mass of at least 25 short tons. Shown here is 1896 diagram of the A. excelsus (then Brontosaurus) skeleton by O.C. Marsh. The head is based on material now assigned to Brachiosaurus sp.