Excalibosaurus (meaning "Excalibur's lizard") is a monotypic genus of marine prehistoric fish-like reptiles (ichthyosaurs) that lived during the Sinemurian stage (approximately 196.5 ± 2 Ma to 189.6 ± 1.5 Ma (million years ago)) of the Early Jurassic period in what is now England. It is characterized by the extreme elongation of the rostrum, with the lower jaw about three fourth of the length of the upper jaw, giving the animal a swordfish-like look. The only known species is Excalibosaurus costini.