Did you know that a Mamenchisaurus lived about 155,000,000 years ago! That was alomost the end of the jurassic period. Mamenchisaurus means mamen reptile. it was about 80 ft long or 25 meters wow! it was 30000.00 pounds or 15000.00 kilograms. Thats heavy. A Mamenchisaurus was a large plant eater. The group it was placed in was called the Sauropoda. The Mamenchisaurus lived in Asia and in China.