Mamenchisaurus likely had two major ways to defend itself: its size and its long tail. The latter was probably used to ward off rivals, to protect itself from predators and to balance the dinosaur's unusually long neck.
Mamenchisaurus was a browsing dinosaur of the family Diplodocidae that lived in Mongolia during the late Jurassic period. These dinosaurs had very long necks and long tails, tiny heads and slender legs. Their bodies had a strong yet relatively lightweight complex skeletal structure.
Mamenchisaurus is famous for having an unusually long neck, even among its long-necked cousins. The neck makes up almost half of the animal's body length and is so unusual that many scientists believe Mamenchisaurus belongs in its own family. The neck had 19 elongated vertebrae. Struts made sure that the neck was held horizontally and stiff while the animal walked, which meant it could only move its head and its shoulders. The long neck is thought to have been used to reach areas that other animals its size could not, such as swamps and dense woodlands
Mamenchisaurus could grow to about 80 feet long. Its neck probably helped it reach high branches of the trees it browsed on, especially if it reared up on its hind legs. At such heights, the leaves of the trees would be new and tender.