Genus: Osmakasaurus McDONALD, 2011
Etymology: From the language of the Lakota People, osmaka, "canyon"; in reference to the name of the type locality in western South Dakota, an area inhabited by the Lakota, and Greek, saurus, "lizard." The generic name is masculine.
Species: depressus (GILMORE, 1909) McDONALD, 2011
= Camptosaurus? depressus GILMORE, 1909
Etymology: Latin, depressa, "pushed down."
= Planicoxa depressa (GILMORE, 1909) Di CROCE & CARPENTER, 2001
Holotype: USNM 4753
Locality: Calico Canyon near Buffalo Gap, (Fall River County, Ostrom, 1965), Custer County, sec. 2, T7S, R5E, South Dakota.
Horizon: Lakota Sandstone.
Age: Barremian Stage, Lower Gallic Subepoch, Middle Early Cretaceous Epoch, Early Cretaceous.
Material: Portions of both ilia, anterior part of the blade of one pubis,
an incomplete sacrum, centrum of the last sacro-dorsal, 12 caudal vertebrae,
1 thoracic rib and many fragments.
Note: Found with Hoplitosaurus marshi.
Locality: Reed's YPM Quarry 13, T22N, R76W, Sec. 4 or 5, Como Bluff, East (East of Marshall road), Albany County, Wyoming.
Horizon: Salt Wash Member, Morrison Formation.
Biostratigraphy: Zone 2.
Age: Comobluffian age, Kimmeridgian Stage, uppermost Malm Epoch, Late Jurassic.
USNM 5820: Anterior portion of a right ilium.
GALTON & JENSEN, 1979
Locality: NW 1/4, NW 1/2, sec. 15, T7S, R6E, Hot springs Quadrangle, Fall River County, South Dakota.
Horizon: Lakota Sandstone, 1 m above the base.
Age: Barremian-Aptian Stage, Gallic Subepoch, Early Cretaceous Epoch, Early Cretaceous.
USGS D262: Partial crown of a right dentary tooth.