Genus: Oligosimus LEIDY, 1872 (nomen dubium)
Etymology: Greek, oligos, “little, few” and Greek, simos, “depressed, concave”: Slightly concave vertebra.

Species: grandaevus LEIDY, 1872
Etymology:

Holotype: USNM 988

Locality: Henry's Fork of Green River, Wyoming.

Horizon:

Biostratigraphy:

Age: Unknown.

Material: Caudal centrum.