This aquatic animal was a nothosaur, an early relative of the plesiosaurs and placodonts. In contrast to the highly modified paddles of plesiosaurs, pachypleurosaurs had hands and feet that were still very similar to those of land-dwelling tetrapods. It is likely that undulations of its backbone provided the main propulsive force for swimming. Like other nothosaurs, Pachypleurosaurus was a marine animal that probably lived on fish or small invertebrates.