Sauropterygia
The earliest sauropterygians appeared about 245 million years ago, at the start of the Triassic period. At first they were small, less than a metre. They were semi-aquatic lizard-like animals with long limbs (called pachypleurosaurs). They developed into a group called the nothosaurs, several meters long. The sauropterygians included another very distinctive group: the placodonts. They were bottom-feeders on shellfish, and possessed flat, crushing teeth to handle their prey.p148–151