Thalassomedon

Thalassomedon is an extinct genus of plesiosaur that lived during the Late Cretaceous period. The name Thalassomedon means "lord of the sea" in Greek. This large marine reptile is known from fossil remains found in the Western Interior Seaway of North America. Thalassomedon belonged to the elasmosaurid family, a group of long-necked plesiosaurs.

The most distinctive feature of Thalassomedon was its exceptionally long neck, which contained a remarkable number of cervical vertebrae, possibly more than seventy. This elongated neck allowed it to hunt prey in the water with a snakelike motion. Its body was broad and flat, supported by four powerful flippers that propelled it through the water. The skull was relatively small compared to its body size and featured numerous sharp, conical teeth, indicating a diet of fish and squid.

Fossils of Thalassomedon have been discovered in states like Colorado and Wyoming, providing valuable insights into the marine ecosystems of that era. Its presence in the Western Interior Seaway, a vast inland sea that once divided North America, suggests it was a successful predator in this environment. The discovery of its fossils has contributed significantly to our understanding of plesiosaur evolution and the diversity of life in prehistoric oceans.