Mamenchisaurus 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 age of late Jurassic Period in China.
Thought to have been extinct for 145 million years, there are still some that remain alive on Primeval Island. In fact, they are one of the largest animals on the Island, alongside Apatosaurus, Brachiosaurus, Diplodocus, Megatherium, and the Woolly Mammoth. They are also among the most common sauropods on the island, alongside Apatosaurus Diplodocus, and Brachiosaurus.