Genus: Styxosaurus WELLES, 1943
Etymology: Styx, mythological 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.
= Hydralmosaurus WELLES, 1943
Etymology: Greek, hydralme, “salt water” and Greek, sauros, “lizard”:
Salt water lizard.
= Thalassonomosaurus WELLES, 1943
Etymology: Greek, thalassa, “sea”, Greek, nomo, “dwell”
and Greek, sauros, “lizard”: Sea-living lizard.
Species: snowii (WILLISTON, 1890) WELLES, 1943
Etymology:
= Cimoliasaurus snowii WILLISTON, 1890
= Elasmosaurus snowii (WILLISTON, 1890) WILLISTON, 1906
Holotype: KUVP 1301
Locality: Hell Creek, Logan County (was Plum County), Kansas.
Horizon: Niobrara Formation, or Upper Smoky Hill Member.
Biostratigraphy: Spinaptychus sternbergi or Hesperornis zone.
Age: Santonian Stage, or basal Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Triassic.
Material: Skull and 28 cervical vertebrae.
WELLES, 1943, Holotype: DMNH 1588; A) right lateral and B) left lateral views.
Modifed from WELLES, 1943, Holotype: DMNH 1588; A) right lateral mouth closed and B) right lateral with mouth open.
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 (95) and fragments of Enchodus.WILLISTON & MOODIE, 1917
= Ogmodirus ischiadicus referred material
WILLISTON 1906
= Styxosaurus snowii WELLES 1943 referred material.Locality: Plum Creek, Logan County, Western Kansas.
Horizon: Niobrara Formation or Upper Smoky Hill Member.
Biostratigraphy: Spinaptychus sternbergi or Hesperornis zone.
Age: Basal Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.
Material:
YPM 1644 (YPM 636): Scapulae, coracoids, pubes and vertebrae.
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Species: marshii (WILLISTON, 1906) emend OTERO, 2016
= Elasmosaurus marshii WILLISTON, 1906 (nomen dubium)
Etymology: In honor of Othneil Charles Marsh.
= Thalassonomosaurus marshii (WILLISTON, 1906) WELLES, 1943 (nomen dubium)
Note:
Otero (2016) placed Thalassonomosaurus marshi in Styxosaurus sp. However, because there is an
assigned species name to the specimen, the name should be Styxosaurus
marshii not Styxosaurus sp.
Locality: Logan County, Kansas.
Horizon: Niobrara Formation or Upper Smoky Hill Member.
Biostratigraphy: Spinaptychus sternbergi or Hesperornis zone.
Age: Basal Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.
Material: 14 vertebral centra (cervical, pectoral and dorsal, listed as 32 or 33, but the difference now cannot be accounted for [STORRS, 1999]), numerous spine, centrum and rib fragments, left scapula, and a nearly complete left fore limb, numerous tiny girdle fragments.
Referred material:
YPM 2062: Scapulae.
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Species: pembertoni (WELLES & BUMP, 1949) emend OTERO, 2016
= Alzadasaurus pembertoni WELLES & BUMP, 1949
Etymology:
Note:
Otero (2016) placed Alzadasaurus pembertoni in Styxosaurus sp. However, because there is an
assigned species name to the specimen, the name should be Styxosaurus
pembertoni not Styxosaurus sp.
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.
Note: Paleopathology, humerus shows avascular necrosis (ROTHSCHILDS & STORRS,
2003)
Referred material:
= Alzadasaurus cf. pembertoni NICHOLLS, 1988
Locality: Manitoba Province, Canada.
Horizon: Pembina Member, Pierre Shale.
Biostratigraphy:
Age: Campanian Stage, Upper Senonian Subepoch, Upper Gulf Epoch, Late Cretaceous.
Material:
P83.02.18: Disarticulated specimen.
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Species: kansasensis (WELLES, 1952) emend OTERO, 2016
= Alzadasaurus kansasensis WELLES, 1952
Etymology: In reference to the state of Kansas, where the specimen was found.
Note:
Otero (2016) placed Alzadasaurus kansensis in Styxosaurus sp. However, because there is an
assigned species name to the specimen, the name should be Styxosaurus
kansasensis not Styxosaurus sp.
Holotype: YPM 1130
Locality: Probably along the Smoky Hill River, Logan County, Kansas.
Note: Was thought to be Wallace County, Kansas.
Horizon: Smoky Hill Member, Niobrara Formation.
Biostratigraphy: Hesperornis zone.
Age: Santonian or Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.
Material: 28 cervicals, 5 pectorals, 3 dorsals, 5 sacrals, 22 caudal vertebrae, associated spine and other vertebral fragments, rib fragments, the nearly complete right rear limb, 6 isolated phalanges, and most of the pelvis.
Referred material:
= Elasmosaurus ischiadicus WILLISTON, 1906 (Referred specimen.)
= Ogmodirus ischiadicus WILLISTON & MOODIE, 1917 (Referred specimen.)Pelvis.
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Species: serpentinus (COPE, 1871) emend OTERO, 2016
Etymology:
= Elasmosaurus serpentinus COPE, 1871
= Hydralmosaurus serpentinus (COPE, 1871) WELLES, 1943
Note:
Otero (2016) placed Hydralmosaurus serpentinus in Styxosaurus sp. However, because there is an
assigned species name to the specimen, the name should be Styxosaurus
serpentinus not Styxosaurus sp.
Holotype: AMNH 1495
Locality: A bluff of blue shale in Cedar, Dixon or Dakota County, Nebraska on the southwest side of the Missouri River between Yankton, South Dakota and Sioux City, Iowa.
Horizon: Smoky Hill Member, Niobrara Formation.
Biostratigraphy:
Age: Santonian or Campanian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.
Material: 58 cervicals, 3 pectorals, 19 dorsals, 4 sacral, 20 caudal vertebrae, coracoid, humerus, femur, and fragmentary pectoral girdle.
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Species: browni WELLES, 1952
Etymology:
Holotype: AMNH 5835
Locality: Red Bird, Niobrara County, Wyoming.
Note: Note Mule Creek, 15 miles west of Edgemont, South Dakota as reported
by WELLES, 1952, as per CARPENTER, 1999.
Horizon: Sharon Springs Member, Pierre Shale.
Biostratigraphy:
Age: Upper Lower to Lower Middle Campanian Stage, Senonian Subepoch, Upper Gulf Epoch, Late Cretaceous.
Material: Skull, 75 vertebrae, pectrum and a pectoral limb.
Skull modified from WELLES, 1943: A) jaws closed and B) jaws opened.
Referred material:
BROWN, 1904
Locality: Head of Hat Creek Basin, 18 miles, southwest of Edgemont, Fall River 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
Note: Now believed to be from the Younger Pierre Shale (MARTIN, SCHUMACHER PARRIS & GRANDSTAFF, 1998)Material:
AMNH 5803: Fragmentary skeleton with gastroliths.
Note: Pteranodon sp found in the stomach region along with a teleost fish, Scaphites and gastroliths (CICIMURRI & EVERHART, 2001).
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Species: rezaci SMITH & O’KEEFE, 2024
Etymology: In honor of the Rezac family of Valparaiso, Nebraska, USA, who graciously donated the specimen to the Univeristy of Nebraska.
= Thalassomedon haningtoni CARPENTER, 1999
Holotype: USNM 50132
Locality: From the property of the Adolph Rezac Family farm, Valparaiso, Saunders County, Nebraska.
Horizon: Graneros shale.
Biostratigraphy:
Age: Lower Cenomanian Stage, Upper Middle Gallic Subepoch, Lowermost Gulf Epoch, Middle Cretaceous.
Material: Complete skull with brittle deformaiton, a complete series of 63 cervical vertebfae, 3 dorsal vertebrae, and a forelimb.
Note: Cephalopods and gastroliths found in the stomach region (CICIMURRI & EVERHART,
2001).
Styxosaurus rezaci after SMITH & O’KEEFE, 2024
Styxosaurus rezaci modified from SMITH & O’KEEFE, 2024: A) skull with mouth closed and B) skull with mouth open.
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