Umoonasaurus possesses the unique-derived features (within Plesiosauria) of thin, arching crests on the
midline of the snout (an elaboration of the midline ridge) and above the orbits, a large triangular pineal
opening bordered by high fluted, crest-like margins. It further differs from all other plesiosaurs in displaying
a distinctive mosaic of primitive and derived features (see character matrix in electronic supplementary material).

Umoona (Antakirinja) indigenous name for the Coober Pedy area, and sauros (Greek), lizard;