Check out this giangantic fossil Ichthyosaur that was recently uncovered in England. I saw this in a NY Time article, which may be read here. (There may be a paywall if you are not a subscriber - sorry). The specimen comes from Jurassic-age rocks, about 180 million years old. It was only discovered as part of landscaping project at the Rutland Water Nature Preserve in the East Midlands. The lagoon had been partially drained when a naturalist saw vertebrae poking out of the lagoon mud. The fossil has now been excavated and the lagoon refilled. If you are able to access the NY Times article, there is a nice video of the specimen by drone, which gives a spectacular view of its immense size within the entire site.
An example of one species of Ichthyosaur recovered from Triassic rocks in Nevada.