Ornithopsis (meaning "bird-likeness") is a genus of sauropod dinosaur, from the Early Cretaceous of England and possibly Germany.

[5] Gideon Algernon Mantell described many fossils that had been previously collected from the Tilgate Forest of the Early Cretaceous Wealden Formation in his 1833 paper on the geology of southeast England, including a bone he considered to be the quadrate of Iguanodon, otherwise only known definitively from teeth that had been found in the area since 1822.

For BMNH R28632, Owen named the new species Bothriospondylus magnus, as he did not consider the two Wealden vertebrae to belong to the same taxon.

[4] Though William Blows identified in 1995 that most of the Wealden sauropod material has been designated as dubious or intermediate, the type vertebra of Ornithopsis shows unique features in its lateral compression and a ventral ridge, and represents a diagnostic titanosauriform.

[10][5] In 2023, a fragmentary dorsal vertebra from the Balve in northwestern Germany, preserved in limestone dating to the Late Barremian-Early Aptian, was described.

[11] Hulke described pelvis material, BMNH R97, from the Wealden in 1882, found associated with a few vertebrae, as the new species Ornithopsis eucamerotus.

He retained Eucamerotus and Chondrosteosaurus as synonyms of Ornithopsis, but suggested that O. hulkei should only contain the original vertebra BMNH R2239.

[9] Hulke described more material as Ornithopsis in 1887, for some vertebrae, ribs, a pelvis, and fragments collected in the Eyesbury Jurassic deposits of Northamptonshire by Alfred Nicholson Leeds.

[14] Hulke described a humerus found in 1868 by J.C. Mansel in the Kimmeridge Clay in 1869, considering it a large saurian possibly related to Cetiosaurus or Pelorosaurus.

greppini, with the genus representing taxon within Cetiosauridae alongside Cetiosaurus, Bothriospondylus, Pelorosaurus, Dinodocus, and possibly Rhoetosaurus and "Morosaurus" brevis.

[22] Later in the same year, Huene revised his classification, naming the new genus Cetiosauriscus for O. leedsii as described by Woodward, and O.

It is narrow, tall, has a ridge on the underside, is opisthocoelous and has a posteriorly placed deep subtriangular pleurocoel over two thirds of its length.