Cymbospondylus is a large ichtyosaur that lived in the Triassic but it's not the largest.
In Zoo Tycoon 2
It is present in the pack Formidable Seas, currently cancelled. In the pirated download it is relatively decently made, if your suspension of disbelief is going to allow the glitch of not being named. Considering how the pack has been fused with Cretaceous Calamity, a fully decent version of the download will never be present, as it Cymbospondylus lived in the Triassic, not in the Cretaceous period. It's also apper in "Park Builder" pack.