Pleurosaurus

Pleurosaurus is an extinct genus of diapsid reptile belonging to the order Sphenodontia, and therefore related to the modern tuatara. Pleurosaurus fossils were discovered in the Solnhofen limestone formation of Bavaria, Germany and at Canjuers in SE France.

Description
Pleurosaurus is one of the few known aquatic sphenodontians. Its body was approximately 60 centimetres (2.0 ft) long, and elongated for hydrodynamic streamlining, with comparatively short limbs and a powerful tail. It would have been able to swim rapidly, by undulating its slender body in a snake-like fashion. It had only small limbs, which probably did not aid in swimming, and nostrils placed far back on the head, close to the eyes.