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 1 to 2 metres (3 to 7 ft) in length, up to a maximum 3 metres (10 ft) long. They are found in marine sediments of the Middle and Upper Triassic, 235–250 million years ago.
The first specimen was discovered in 1830, and the group was very widely distributed. Shellfish were common throughout the Mesozoic period, but this group of shellfish-eaters went extinct at the end of the Triassic. They were clearly a victim of some event which disturbed their lifestyle. The end-Triassic had several extinction events which are not well understood.