Brachiosaurus and Apatosaurus are probably the most famous sauropods, or "long necks," of the Mesozoic Era. But Mamenchisaurus deserves some love for taking neck length to the extreme. This dinosaur evolved the most ridiculously extended neck of any sauropod, about 35-40 feet. In fact, the Mamenchisaurus' neck was so freaking huge that it couldn't hold its head in the tree tops (you try pumping blood 40 feet high!) but rather swept its mouth through underbrush like the world's weirdest-looking vacuum cleaner. Artwork by AshiRox.