[1][2] It can be distinguished from all other iguanodontians by the presence of a prominent ridge on the sternal process of the coracoid and an oval muscle scar on the front of the deltopectoral crest of the humerus.

[2] Cumnoria is known from the holotype OXFUM J.3303, a partial skull and postcranium, recovered from the lower Kimmeridge Clay Formation, in the Chawley Brick Pits, Cumnor Hurst.

Workers at first discarded the remains on a dump heap, but one of them later collected the bones in a sack and showed them to Professor George Rolleston, an anatomist at the nearby Oxford University.

In the new analyses of McDonald Cumnoria has instead been recovered as a basal member of the Styracosterna, more closely related to more derived ("advanced") iguanodontians than to Camptosaurus dispar.

[2] Rhabdodon spp Zalmoxes robustus Zalmoxes shqiperorum Tenontosaurus tilletti Dryosaurus altus Dysalotosaurus lettowvorbecki Valdosaurus canaliculatus Cumnoria prestwichii Camptosaurus dispar Uteodon aphanoecetes Dakotadon lakotaensis Hippodraco scutodens Iguanacolossus fortis Proa valdearinnoensis Lanzhousaurus magnidens Hypselospinus fittoni Bayannurosaurus perfectus Ouranosaurus nigeriensis Hadrosauroidea