Family Camarasauridae

Members of this family were much smaller than their contemporaries, the brachiosaurs and diplodocids. Their necks and tails were shorter, and their skulls were higher, with blunter snouts. The teeth, too, were quite different from those of other sauropods; they were long, spoon-shaped and forward-pointing.

All these features suggest that the camarasaurs ate different plants from the larger sauropods in the locality, and so did not compete with them for food.

name: Camarasaurus time: Late Jurassic locality: North America (Colorado,

Oklahoma, Utah and Wyoming) size: up to 59 ft/18 m long

This ubiquitous sauropod probably roamed in herds over the moist, tropical plains that covered western North America during the Jurassic period. Its heavy, spoon-shaped teeth could have dealt with fibrous plants, such as ferns and horsetails. And it could have reached up to the lower branches of conifer trees, and torn away great mouthfuls of tough, needlelike leaves.

Camarasaurus had enormous nasal openings on top of its skull. Their size, together with the animal's short face, has led some paleontologists to speculate that this sauropod had a trunk, like that of a modern elephant, and used it in the same way. However, other scientists think that the large nasal openings acted as a cooling device for the brain (see Brachiosaurus, above).

The remains of juveniles have been found with adult Camarasaurus in the same sequence of rocks (known as the Morrison Formation) in the western USA. This suggests that the young traveled with the herd, maybe on long migrations if the animals were forced to find new feeding grounds. The periodic droughts typical of this tropical Jurassic land could have made such migrations necessary.

Another clue to lifestyle is found in the isolated heaps of polished pebbles preserved in the same rocks. These could be the regurgitated stomach stones that many sauropods, including

Camarasaurus, swallowed as an aid to grinding up their tough plant food. Many modern birds also swallow stones for the same reason. When the stones have become so worn as to be of little use as digestive aids, they are regurgitated and new ones are found.

name: Euhelopus time: Late Jurassic or Early

Cretaceous locality: Asia (China) size: 49 ft/15 m long Although Euhelopus and Camarasaurus lived on opposite sides of the world, the two sauropods were closely related and of similar build.

There were some differences, however. For example, Euhelopus had a much longer neck, made up of 17-19 elongated vertebrae (Camarasaurus had a short neck, with only about 12 vertebrae). Nor did Euhelopus have the "pug nose" of its relative; its head was longer, with a more pointed snout. But like Camarasaurus, it had the same heavy, spoon-shaped teeth, and large nasal openings on top of its head.

name: Opisthocoelicaudia time: Late Cretaceous locality: Asia (Mongolia) size: possibly 40 ft/12.2 m long

The exact size and appearance of this sauropod can only be guessed at, since the one skeleton unearthed in the Gobi Desert of Mongolia was missing the neck and head. However, the rest of the body was well preserved, and seems to be that of a typical, though relatively small and streamlined, camarasaur.

It is the way in which the tail vertebrae lock together that sets Opisthocoelicaudia apart from all other known sauropods. Usually, a sauropod's vertebrae are hollowed out on their front ends (ie concave toward the animal's head), and they lock together in a forward-pointing arrangement. The tail vertebrae of Opisthocoelicaudia, however, are concave on their rear faces, and lock together in a backward-pointing direction, toward the tip of the tail. This feature gives the animal its name, which means "tail bones hollow at the back."

The peculiar articulation of Opisthocoelicaudia's tail formed a powerful and rigid arrangement. Some paleontologists have suggested that the tail was used as a body prop, a "third leg," to steady the animal when it reared up on hindlegs to feed on the topmost branches of trees. Other sauropod dinosaurs, such as the diplodocids and the titanosaurs (see pp. 132-133), seem to have used their tails to prop themselves up in the same way.

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