Prehistoric marine reptiles were not just limited to mosasaurs, plesiosaurs, and ichthyosaurs. There were some who were crocodilians who were specially adapted to life in the sea. One such example is Metriorhynchus. Despite being a crocodilian, Metriorhynchus has evolved traits that were similar to the more traditional marine reptiles it swam alongside. This includes flippers instead of feet and a distinctive tail fluke.
Grady P Brown - Author 