[4] Other remains suggested to be closely related to Opisthias are also known from the Late Jurassic Alcobaça Formation of Portugal.

[5][6] An undescribed crushed skull (DINO 16454) from the Morrison Formation has been attributed to this genus by some sources, though this has been strongly disputed by others.

[7] A lower jaw is also known from the Berriasian aged Lulworth Formation of the United Kingdom, which appears to be distinct from the type North American species.

[8] A fragmentary dentary possibly attributable to Opisthias is also known from the Berriasian aged Angeac-Charente bonebed in France.

[9] Opisthias has been interpreted as a generalist, with its tooth morphology indicating had an ability to process plant material.