According to an article from Scientific American, the fossil of a young Plesiosaur has been found in Antarctica.
Plesiosaurs, for those of you who do not know (and I didn't until I looked it up in the library's copy of the Kingfisher Illustrated Dinosaur Encyclopedia), were sea reptiles that flourished in the Jurassic period. According to the Kingfisher encyclopedia, plesiosaurs had "four flipperlike fins, and they swam by beating these up and down like wings, instead of by waving their tails." According to the encyclopedia, fossils of the Plesiosaurus had only previously been found in Europe.
Read more about Plesiosaurs at Enchanted Learning.