Mamenchisaurus was a large, long-necked dinosaur that lived during the Late Jurassic period, around 160 million years ago. It was primarily found in what is now China. This dinosaur is known for its exceptionally long neck, which could reach lengths of up to 30 feet, making it one of the longest-necked dinosaurs ever discovered. Mamenchisaurus belonged to the group of dinosaurs called sauropods, which were characterized by their massive bodies and long tails. It likely fed on vegetation from tall trees, using its long neck to reach leaves that other herbivores could not. Its fossils have provided valuable insights into the diversity of dinosaurs during the Jurassic era.