Ornithopsis (meaning "bird-likeness") was a medium-sized Early Cretaceous sauropod dinosaur, from England. The type species, which is the only species seen as valid today, is O. hulkei. History of discovery 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 of Iguanodon, otherwise only known definitively from teeth that had been found in the area since 1822. The bone was redescribed by Richard Owen in 1854, who reaffirmed its referral as a quadrate of Iguanodon, but also suggested it could be the same bone of Streptospondylus or Cetiosaurus as it was not directly associated with the characteristic teeth of Iguanodon. This specimen is stored as British Museum of Natural History R2239, having been purchased from Mantell in 1838. BMNH R28632, a similar bone to BMNH R2239 was described in 1870 by Harry Govier Seeley, found in the deposits on the Isle of Wight and purchased from Mantell by the British Museum in 1853. Seeley properly identified the two fossils as , and noted that the features considered by Mantell and Owen to indicate the tympanic cavity was in fact openings in the walls of the vertebral , showing that the bones were invaded by cavities for air sacs as seen in both pterosaurs and modern birds. Seeley gave the name Ornithopsis hulkei for the vertebrae, named in honour of his colleague John Whitaker Hulke, considering the taxon to be between pterosaurs and birds, and possibly allied with dinosaurs. The genus name is derived from Greek , "bird" and , "likeness". Owen revisisted the material in 1875, where he described multiple new species within his new genus Bothriospondylus. Agreeing with the vertebral identity of BMNH R2239, but considering it closer to the type species Bothriospondylus suffossus than any flying animal as Seeley had suggested, Owen gave the new species name Bothriospondylus elongatus for the specimen. 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. Owen heavily disagreed with the interpretations of Seeley that the vertebrae were open and lightly constructed and showed relationships to birds and pterosaurs, considering the name Ornithopsis to be glaringly false and thus suggesting his new names should have priority over Seeley's