saur·op·ter·yg·i·an 
(sô-rŏp′tə-rĭjē-ən)
(sô-rŏp′tə-rĭjē-ən)n.
Any of various extinct aquatic reptiles of the group Sauropterygia that flourished during the Mesozoic Era and included the plesiosaurs.
[From New Latin Sauropterygia, superorder name : Greek sauros, lizard + Greek pterux, pterug-, wing, flipper; see pet- in the Appendix of Indo-European roots.]
saur·op′ter·ygi·an adj.