NEBRASKA ON THE SOUTHWEST SIDE OF THE MISSOURI RIVER BETWEEN YANKTON, SOUTH DAKOTA AND SIOUX CITY, IOWA.

DIXON OR DAKOTA COUNTY

A BLUFF OF BLUE SHALE IN CEDAR

SMOKY HILL MEMBER

NIOBRARA FORMATION

SANTONIAN OR CAMPANIAN STAGE

SENONIAN SUBEPOCH

GULF EPOCH

LATE CRETACEOUS
STEM: TETRAPODA GOODRICH, 1930
SUPERCLASS: AMNIOTA HAECKEL, 1866

CLASS: REPTILIA LAURENTI, 1768

SUBCLASS: DIAPSIDA

NEODIAPSIDA: BENTON, 1985

LEPIDOSAUROMORPHA: BENTON 1985

INFRACLASS: EURYAPSIDA COLBERT, 1945

SUPERORDER: SAUROPTERYGIA OWEN 1860

GRANDORDER: EOSAUROPTERYGIA emend RIEPPEL, 1994

ORDER: PLESIOSAURIA OWEN, 1840 NON BLAINVILLE, 1835

SUBORDER: PLESIOSAURIA OWEN, 1840 NON BLAINVILLE, 1835

INFRAORDER: PLESIOSAUROMORPHA NOVA

EUPLESIOSAURIA O’KEEFE, 2001

Superfamily: ELASMOSAUROIDEA Cope, 1869

Family: ELASMOSAURIDAE Cope, 1869

*Hydralmosaurus serpentinus
= Elasmosaurus serpentinus