Mamenchisaurus had the longest neck of any known animal ever, reaching up to 50 feet long (almost half the length of its whole body!). This huge neck was made lighter by air sacs in the cervical vertebrae (neck bones).

Having such a long neck meant it did not need to spend as much energy walking around to find food. Once it finished grazing in one area, Mamenchisaurus simply swung its lengthy neck around to graze in a new spot.