Placodont
Placodonts were a group of Triassic marine reptiles which had heavy flat teeth. These teeth were used for crushing shellfish. Placodonts are in the Order Sauropterygia, the group that includes Plesiosaurs. Placodonts were mostly between  in length, up to a maximum  long. They are found in marine sediments of the Middle and Upper Triassic, 235–250 million years ago.