In terms of physical shape, the plesiosaurs are unique. They had a squat rump, a snake-like neck and four roughly equally sized paddles. Only 13 complete specimens and scattered remains of plesiosaurs have so far been found in the Posidonia shale of Holzmaden.
The plesiosaurs were “lurking predators”. When they hunted for fish or squid, their small head at the end of their long and extremely flexible neck allowed them to easily grasp their prey from the scattering swarms. It has not been established whether the plesiosaurs could drag themselves onto the land to lay their eggs, like the sea turtles, or whether they bore their young in the water, like the ichthyosaurs.
You can take a closer look at the plesiosaurs in this interactive 3D film.