Thalassomedon

Thalassomedon is a genus of plesiosaur, named by Welles in 1943. Greek, thalassa, "sea", and Greek, medon, "lord, ruler": Sea lord.

Introduction
This genus of plesiosaur occurred in North America about 95 Ma. It occurs in the Cenomanian strata of the Late Cretaceous rock. Its closest relative is the Elasmosaurus, and together they make up the family Elasmosauridae. There are six specimens of varying state of preservation on display at various U.S. museums.

Anatomy
With a length of 12 meters (40 ft), the neck comprises 63 vertebrae about 6 meters (20 ft) or half the creature. Skull is 47 centimeters (18.7 in) long, with 5 cm (2 in) teeth. The flippers were about 1.5-2 meters (5-7 ft) long. Stones have been found in its stomach area leading some to theorise that they were used for ballast or digestion: when the stones are moved by stomach action, the food is ground up.