Genus: Thalassomeodon WELLES, 1943
Etymology: Greek, thalassa, “sea”, and Greek, medon, “lord, ruler”: Sea lord.
= Alzadasaurus WELLES 1943 (partim)
Etymology: In reference to the town of Alzada, Montana, near where the specimen was found, Greek, sauros, “lizard”: Alzada lizard.

Species: haningtoni WELLES, 1943
Etymology:

Holotype: DMNH 1588

Locality: On a small, intermittent and unnamed creek in northwestern Baca County, Colorado.

Horizon: Graneros shalle.

Biostratigraphy:

Age: Lower Cenomanian Stage, Upper Middle Gallic Subepoch, Lowermost Gulf Epoch, Middle Cretaceous.
Note: Was Lowest Formation in the Benton Group, Early Late Cretaceous.

Material: Skull and skeleton.

Thalassomeodon haningtoni WELLES, 1943, Holotype: DMNH 1588; A) right lateral and B) left lateral views.

Reconstruction of the skull WELLES, 1943, Holotype: DMNH 1588; A) closed mouth, and B) open mouth.

 

Referred material:


= Alzadasaurus riggsi WELLES, 1943
Etymology:
= Elasmosaurus serpentinus Fide RIGGS, 1939

Holotype: FMNH P 12009

Locality: Alzada, Carter County, Montana.

Horizon: Belle Fourche Formation.

Biostratigraphy:

Age: Early Cenomanian Stage, Upper Middle Gallic Subepoch, Lowermost Gulf Epoch, Middle Cretaceous.
Note: Was Benton Formation, Turonian, Late Cretaceous.

Material: 60 or more vertebrae, both scapulae, coracoids, the left paddle almost complete, left pubis, and both ischia and ilia.
Note: 206 granite gastroliths.