What are the ichthyosaurus and plesiosaurus?

PlesiOSaurs and icthyosaurs were two unrelated groups of marine reptiles that lived during the Mesozoic. PlesiOSaurs had long necks and short tails, or short necks and long tails, and they propelled themselves using their flippers. Icthyosaurs were reptiles that looked much like fish, with a long narrow snout, and a vertical tail fin. Both plesiOSaurs and icthyosaurs ate marine animals.