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Thalassomedon (from Greek, thalassa, "sea" and Greek, medon, "lord" or "ruler", meaning "sea lord") is a genus of plesiosaur, named by Welles in 1943.

Temporal range: Late Cretaceous, 95 Ma
Mounted cast of the type specimen, American Museum of Natural History
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Family: Elasmosauridae
Genus: Thalassomedon
Welles, 1943
T. haningtoni
Binomial name
Thalassomedon haningtoni
Welles, 1943
  • Alzadasaurus riggsi Welles, 1943




Thalassomedon is among the largest elasmosaurids, with a total length of 10.86 metres (35.6 ft) for the holotype.[1] There is a larger skull however suggesting a much larger animal, potentially up to 11.7 metres (38 ft).[2] The neck is also very long; it comprises 62 vertebrae[3] and is about 5.9 metres (19 ft) - over half of the total length. The skull is 47 centimetres (19 in) long, with 5 centimetres (2.0 in) long teeth. The flippers were about 1.5–2 metres (4.9–6.6 ft) 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.


Neck vertebrae

This genus of plesiosaur lived in North America, approximately 95 million years ago - this places it during the Cenomanian stage. Its closest relative is Elasmosaurus, and both belong to the family Elasmosauridae. There are six specimens of varying states of preservation on display at various museums in the United States.

See alsoEdit


  1. ^ O'Gorman, J.P. (2016). "A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids". Ameghiniana. 53 (3): 245–268. doi:10.5710/AMGH.29.11.2015.2928.
  2. ^
  3. ^ Carpenter, K. (1999). "Revision of North American elasmosaurs from the Cretaceous western interior." Paludicola, 2(2): 148-173.

External linksEdit