| Named By: | C. C. Young in 1954 |
| Time Period: | Late Jurassic, 160-145 Ma |
| Location: | China |
| Size: | Up to 35 meters long for the largest species M. sinocanadorum |
| Diet: | unavailable |
| Fossil(s): | Several individuals are known, although usually from partial remains |
| Classification: | | Chordata | Rreptilia | Dinosauria | Saurischia | Sauropodomorpha | Sauropoda | Mamenchisauridae | |
| Also known as: | | Zigongosaurus | |
Mamenchisaurus ( mah-MUN-chi-SAWR-as,[1] or spelling pronunciation ) is a sauropod dinosaur genus including several species, known for their remarkably long necks which made up half the total body length. It is known from numerous species which ranged in time from 160 to 145 million years ago, from the Oxfordian to Tithonian ages of the late Jurassic Period of China, and the largest species may have reached 35 m (115 ft) in length and possibly weighed 50 to 75 tons.