Mamenchisaurus, meaning “Mamenchi lizard” (from the Chinese words ma: “horse”, men: “gate”, and chi: “brook”), is a genus of dinosaur from the Tithonian age of the Late Jurassic Period (150 to 145 million years ago). It was first discovered in 1952 on a highway construction site in Sichuan, China. It was studied and named in 1954 by paleontologist Professor C.C. Young. A second specimen was discovered in 1972 in the United States. The type species, M. constructus, was named in honor of where the dinosaur was found; on a construction site. There are 5 known species of Mamenchisaurus (M. constructus, M. anyuensis, M. hochuanensis, M. sinocanadorum, and M. youngi). Another species, M. fuxiensis, possibly belongs in a different genera.
Mamenchisaurus was a four-legged herbivore, known for its rather long neck. The type species, M. constructus, measured 72 feet in length, of which nearly half of that was its neck. It had the longest known neck of any animal at that time. It had 19 vertebrae in the neck spine. Based on fossils recovered, the average length of the neck of this dinosaur would have been between 31 feet and 46 feet long. It also had the longest cervical rib of any creature living at that time, and also the longest of any sauropod dinosaur that has been described. The rib was 13.5 feet long.