Thalassomedon was a plesiosaur, a type of marine reptile. It was not a dinosaur, though it coexisted with many dinosaurs. Thalassomedon lived during the Late Cretaceous.
All these Thalassomedon pictures were collected from the internet. Enjoy and explore:
- S. P. Welles. 1943. Elasmosaurid plesiosaurs with description of new material from California and Colorado. Memoirs of the University of California 13:125-254