DIPLODOCUS

genus of extinct giant sauropod dinosaurs found as fossils in Late Jurassic rocks of North America (the Late Jurassic epoch occurred 163 to 144 million years ago). Diplodocus, perhaps the most commonly displayed dinosaur and a relative of Apatosaurus (popularly Brontosaurus), was the longest land animal that ever lived; the longest known was 26.7 m (87.5 feet) long. The skull, unusually small, was elongate and rather light; it sat atop a very long neck. The brain was extremely small. Its relatively light body was well supported by limb girdles and pillarlike legs. While most of these dinosaurs weighed just over 10 tons, some members of the genus may have weighed as much as 80 tons. The tail was very long and probably extremely flexible. It most likely provided an anchoring site for the powerful hind leg muscles; it is also possible that the tail was a defensive weapon that could lash out at predators with great force. A mass of nervous tissue present at the base of the spine aided in the coordination of the movements of the hind limbs and tail. Because the great length of the animal would have made the transmission of nervous impulses from the tiny brain to the hindquarters a slow process, the spinal node, often mistakenly called a second brain, was developed to compensate for the time lag. Some theories suggest that Diplodocus may have spent a good deal of time in the water with only its head sticking out. It is probable that Diplodocus could move about freely on dry land; the limbs were relatively slim and the feet broad, much like those of modern elephants. The character of the teethpencillike, dull-edged, and located on the anterior margins of the jawsindicates that Diplodocus probably fed on soft vegetation.