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.
General shape [change]
By the Upper Triassic, these plates had grown so much that placodonts of the time such as Henodus and Placochelys looked like the sea turtles of modern day more than their ancestors. Other placodonts like Psephoderma developed plates as well, but in a different articulated manner that resembled the shells of horseshoe crabs and trilobites more than those of sea turtles. All these adaptations are examples of convergent evolution, as placodonts were not related to any of these animals.
Because of their dense bone and heavy armour plating, these creatures would have been too heavy to float in the ocean and would have used a lot of energy to reach the water surface. For this reason, and because of the type of sediment found with the fossils, it is suggested placodonts lived in shallow waters and not in deep oceans.
The placodonts ate shellfish. Their front teeth stuck out: they would be used to dig up the shellfish, and pull them from any attachment to the substrate. Inside their mouth, the teeth were large and flat: they were used to crush the shells.
- "Spade-like incisors at the front, for snipping and scraping oysters from the rocks; and broad circular back teeth that acted as a pounding board to crush the shells, before the flesh was swallowed". Benton.p119
- Benton M.J. 1990. The reign of the reptiles. Crescent, New York. 118–122