"Shonisaurus" had a long snout, and its flippers were much longer and narrower than in other ichthyosaurs. While "Shonisaurus" was initially reported to have had socketed teeth (rather than teeth set in a groove as in more advanced forms), these were present only at the jaw tips, and only in the very smallest, juvenile specimens. All of these features suggest that "Shonisaurus" may be a relatively specialised offshoot of the main ichthyosaur evolutionary line. More recent finds however indicate that "Shonisaurus" possessed teeth in all ontogenetic stages. It was historically depicted with a rather rotund body, but studies of its body shape since the early 1990s have shown that the body was much more slender than traditionally thought. "S. popularis" had a relatively deep body compared with related marine reptiles.