Thalassomedon is among the largest elasmosaurids, with an estimated body length of long and body mass of . The neck is also very long; it comprises 62
vertebrae and is about - over half of the total length. The skull is long, with long teeth. The flippers were about long. Stones have been found in its stomach area leading some to theorize that they were used for ballast or
digestion. If the latter, stomach action would cause the stones to help grind ingested food. ==Discovery==