Thalassophonea is an extinct clade of pliosaurids from the Middle Jurassic to the early Late Cretaceous (Callovian - Turonian) of Australia, Europe, North America and South America. Thalassophonea was erected by Roger Benson and Patrick Druckenmiller in 2013. The name is derived from Greek thalassa (θάλασσα), "sea", and phoneus (φονεύς), "murderer". It is a stem-based taxon defined as "all taxa more closely related to Pliosaurus brachydeirus than to Marmornectes candrewi".
The following cladogram follows an analysis by Benson & Druckenmiller (2014).