Apatosaurus was a sauropod that came to dominance in the Jurassic.

Canadian Museum of Nature

Apatosaurus

APATOSAURUS (uh-PAT-oh-SORE-us)

Period: Late Jurassic

Order, Suborder, Family: Saurischia, Sauropodomorpha, Diplodocidae

Location: North America

Length: 70 feet (21 meters)

Apatosaurus moved constantly, feeding day and night. When they walked, the ground, thundered, because each adult weighed as much as five adult elephants. The idea of a thundering walker gave Brontosaurus its name, which means "thunder lizard." The name Apatosaurus was used first for this dinosaur, so it is the correct name. But the literal meaning of its name, "deceitful reptile," is difficult to apply to this giant. With a shoulder height of 12 feet, a length of about 70 feet, and a weight of 30 tons, this peaceful herbivore could neither hide nor disappear into the background.

Like its close relatives Diplodocus, Barosaurus, and Supersaurus, this sauropod had a small bead; a long, slender neck; and a deep, heavy midsection. It also had legs built like pillars and a long heavy tail that ended in a slender whip.

Apatosaurus skull

American Museum of Natural History

A few years ago, one of the most celebrated mistakes in science was found: the wrong head had been placed on the Apatosaurus skeleton in the Carnegie Museum of Natural History in Pittsburgh. A skull of Camarasaurus, which belongs to a different family, was put on the skeleton. The Apatosaurus was nearly complete when if was excavated except that it had no head. The best guess at the time was that its skull was like that of Camarasaurus, with a rounded and blunt profile, large crushing teeth, and powerful jaws. The scientists who discovered the mistake studied the quarry maps where all the bones were found and realized that the skull had slipped a few feet away from the neck before burial and preservation. The actual skull was at the Carnegie Museum. The skull of Apatosaurus turned out to look very much like that of Diplodocus, with a long slender profile and small delicate teeth in the front of the jaws.

The neck of Apatosaurus was small near the head, but the base of the neck near the body was huge, and the neck bones were long and massive. Despite its long neck, Apatosaurus had limited capability for raising its head, which could probably not reach much higher than its shoulders.

The bones of the middle part of the body were huge. Its ribs were long and straight, and its vertebrae (bones of the spine) were huge but had hollow spaces that made them lighter but did not make them less strong. Its legs were straight and massive, like an elephant's, with short stubby toes. The toes of the front feet were blunt, except for the inner toe, which had a claw that pointed inward. The rear feet had three claws that looked a little like a cow's hooves.

Apatosaurus was taller at the hips than the shoulders; the height of a full-grown animal's hips was about 15 feet. Its hips were huge, and the hip sockets had to support the enormous stress of walking with such a heavy body. Its tail bones near the front of its tail were also huge, and all of the tail bones had tall spines where muscles attached for holding it off the ground. The tail probably weighed several tons, and it probably balanced the animal when it walked. The length of the tail, around 30 feet to the tip, helped distribute its weight.

Early paleontologists had many wrong ideas about Apatosaurus. Because of the animals' size, scientists thought they must have lived in water. The animals actually lived in semi-dry places. Their trackways show that they walked on land, and their skeletons show no adaptions for living in water.

For many years, artists and scientists drew Apatosaurus and its relatives with their tails dragging on the ground. But there is no evidence for this; there are no tail marks in sauropod trackways, and there was no wear or damage to the tail bones. Also, a two or three ton tail would have become tangled in plants or caught in cracks in the rocks if it was dragged. Apatosaurus carried its tail high off the ground, with the tail gracefully swaying to help the animal keep its balance.

Another wrong idea came about because the skeleton was mounted wrong. Apatosaurus was put in a sprawling position, which would have meant that it waddled. Trackways prove that sauropods placed their feet almost perfectly under the center of their bodies when they walked. They probably walked as gracefully as elephants, and just as efficiently.

Apatosaurus, like the other sauropods, was a plant-eater. Paleontologists argue about how it could eat enough to keep a 30-ton body alive. The skull and jaws seem too small to keep enough food coming in. Also, the dominant plants of the time, the conifers, were not nutritious enough for these giants. One adaptation that aided their digestion was gastroliths or "stomach stones" that were in their digestive tracts. The dinosaurs swallowed small stones that then helped grind up the plants in their stomachs. Gastroliths are sometimes found in excavations of Apatosaurus and its relatives.

Adult apatosaurs had few enemies, but the younger animals were easy prey for giant predators such as Allosaurus and Ceratosaurus. The young probably stayed close to parents and other adults to protect them from attack. One set of dinosaur tracks in Texas seems to show that in a herd of sauropods traveling together, adults moved on the outside and the younger animals were in the center of the group.

Apatosaurus was one of the most common sauropods. Its remains have been found in Utah, Colorado, and Wyoming, but it may have lived farther south and farther north. Skeletons and restorations of Apatosaurus are among the most common museum exhibits, because only a few other dinosaurs were larger. It is the most studied sauropod.