Genus: Opisthiamimus DeMAR JR, JONES & CARRANO, 2022
Etymology: Opisthias (a genus of the clade Rhynchocephalia) and Greek, mimos, "mimic" (latinized to mimus); referring to the morphological similarities of the dentary and dentary teeth between this taxon and Opisthias.

Species: gregori DeMAR JR, JONES & CARRANO, 2022
Etymology: In honor of Joseph Gregor, a dedicated Smithsonian volunteer who skillfully prepared teh holotype and referred specimens.

Holotype: USNM PAL 772041

Locality: USNM Loclaity 42188 (Fox Mesa Locality), Big Horn County, Wyoming.

Horizon: Morrison Formation.

Biostratigraphy:

Age: Kimmeridgian or Tithonian Stage, Malm Epoch, Late Jurassic.

Material: An articualted partial skull and skeleton.

Referred material:

USNM PAL 720475: Partial skull (left maxilla, jugal, quadrate, and palatine; part of right palatine) and lower jaw (left dentary, angular, surangular, articular and prearticular).

USNM PAL 720475: Partial right dentary wiht 4 teeth.

USNM PAL 720479: Partial atlas/axis complex.