Genus: Styxosaurus WELLES, 1943
Etymology: Styx, mythologicla river in Hades, and Greek, sauros, “lizard”; Styx lizard.
= 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: snowii (WILLISTON, 1890) WELLES, 1943
Etymology:

Referred material:

CICIMURII & EVERHART, 2001

Locality: Logan County, Kansas.

Horizon: Sharon Springs Member, Pierre Shale.

Biostratigraphy:

Age: Upper Lower to Lower Middle Campanian Stage, Senonian Subepoch, Upper Gulf Epoch, Late Cretaceous

Material:

NJSM 15435: Nearly complete skeleton lacking skull.
Note: Gastroliths and fragments of Enchodus.

 

= Alzadasaurus pembertoni WELLES & BUMP, 1949
Etymology:

Holotype: Museum of Geology, South Dakota School of Mines and Technology, No. 451

Locality: 25 miles south of Chamberlain and 11 miles northeast of Iona, Missouri River, Lyman County, South Dakota.

Horizon: Sharon Springs Member, Pierre Shale.

Biostratigraphy:

Age: Upper Lower to Lower Middle Campanian Stage, Senonian Subepoch, Upper Gulf Epoch, Late Cretaceous

Material: Skull and nearly complete skeleton.
Note: Found with 253 quartzite gastroliths.