Placodonts ("Tablet teeth") were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. It is believed that they were part of Sauropterygia, the group that includes plesiosaurs. Placodonts were generally between 1 to 2 metres (3 to 7 ft) in length, with some of the largest measuring 3 metres (10 ft) long.
The first specimen was discovered in 1830, and they have since been discovered throughout central Europe, North Africa, the Middle East and China.
Read more about Placodonts: Palaeobiology, Classification