'Shonisaurus' sikanniensis (Nicholls and Manabe 2004, renamed by Sander et al. 2011) was a giant Late Triassic ichthyosaur at 18-21 meters (69 feet). It did not preserve a rostrum, but no teeth were found with what remained of the giant jaws. Among tested taxa S. sikanniensis nested with Cymbospondylus and Mixosaurus, not the holotype of Shastasaurus pacificus. Nor did it nest with Shonisaurus popularis (see below) as both have a distinct skull and pectoral morphology. Flippers were not preserved but the girdles that were preserved suggest small flippers, especially the hind flippers for which a tiny femur was identified. Sander et al. 2011 considered this specimen conspecific with Shastasaurus, but the two are not related.
'Shonisaurus' sikanniensis, like Cymbospondylus, was derived from a sister to Mixosaurus. S. sikanniensis retaind a large orbit and developed a longer cervical series.