Apatosaurus

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Apatosaurus, a plant-eating dinosaur of the late Jurassic time, was one of the largest land animals that ever lived, perhaps weighing up to 32 metric tons (35 U.S. tons). Here it is compared in size with today's largest land animal, the African elephant. (Grolier Interactive Inc.)

Apatosaurus was one of a number of giant, plant-eating dinosaurs that roamed western North America during the Late Jurassic Period, more than 140 million years ago. The animal probably will remain better known for some time under the name Brontosaurus, because this name has been used in many books and films about dinosaurs. Paleontologists use the name Apatosaurus, however, because the first fossil fragment of the animal was so labeled, and by scientific convention the first name given is the one accepted. Apatosaurus and other giants such as Brachiosaurus, Diplodocus, and Camarasaurus constitute the suborder Sauropoda. These five-toed, long-necked dinosaurs were the dominant herbivores of their time. Their fossils occur in abundance in rock formations in Utah, Colorado, and Wyoming.

Apatosaurus had an enormous, barrellike body supported by thick, heavy legs. Its tail and neck were long and stout. More than 25 m (82 ft) in total length, it weighed 18-32 metric tons (20-35 U.S. tons). The skull was elongated and had short but pointed teeth. Apatosaurus skeletons are usually headless when they are found, however, because of fragile skull and neck connections. When the American paleontologist O. C. Marsh uncovered the first such skeleton, in 1879, he paired it with a wrong skull found nearby — that of the dinosaur now known as Camarasaurus. As a result, Apatosaurus was depicted as having a snub-nosed head with peglike teeth until the late 1970s, when the error was corrected.

Traditionally, paleontologists have regarded Apatosaurus as a semiaquatic animal, feeding and wallowing in lakes, swamps, and rivers. This idea was based on the belief that the animal's enormous weight was too great for the legs to bear and that it therefore needed to live in water to support its weight. Using this line of reasoning, some scientists suggested that the animal's long neck permitted it to breathe while at depths of 6-8 m (20-25 ft). This theory is flawed, however, because water pressures at depths of only a few meters would have been too great to permit the animal to breathe. More recently it has been suggested that all of the sauropods lived on land, using their long necks to reach and browse on treetop foliage.

John H. Ostrom

Bibliography: Alexander, R. McNeill, The Dynamics of Dinosaurs and Other Extinct Giants (1989); Glut, D. F., The Complete Dinosaur Dictionary (1992); Lambert, David, The Dinosaur Data Book (1990); Weishampel, David, et al., eds., The Dinosauria (1990).

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