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. Stegosaurus means "roof lizard" or "plated lizard". One of the various plated dinosaurs (Stegosauria) of the Late Jurassic Period (159 million to 144 million years ago) recognizable by its spiked tail and series of large triangular bony plates along the back. Stegosaurus usually grew to a length of about 21 feet, but some reached 30 feet. The skull and brain were very small for such a large animal. The forelimbs were much shorter than the hind limbs, which gave the back a characteristically arched appearance. The feet were short and broad. They are classified as a quadrupedal herbivorous ornithischian dinosaur.