Skeleton of the now extinct, Archelon Ischyros, the largest sea turtle to have ever lived

Fun fact: this fossil is likely missing a flipper because it was torn off by a mosasaur. Many fossils of Archelon have such injuries, many old-enough to have healed up, meaning they survived the dramatic amputations of their limbs and just kept on trucking.

That is so awesome!

It's how it functions. You'd wind it up and it'd start swimming for a good couple decades.