SOUTH DAKOTA AND SIOUX CITY
IOWAON THE SOUTHWEST SIDE OF THE MISSOURI RIVER BETWEEN YANKTON
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 OSBORN, 1904
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
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