Early paleontologists modelled the body of this small, bipedal, herbivorous dinosaur in various ways. In 1882 Hulke suggested that Hypsilophodon was quadrupedal but also, in view of its grasping hand, able to climb rocks and trees in order to seek shelter. In 1912 this line of thought was further pursued by Austrian paleontologist Othenio Abel. Concluding that the first toe of the foot could function as an opposable hallux, Abel stated that Hypsilophodon was a fully arboreal animal and even that an arboreal lifestyle was primitive for the dinosaurs as a whole.Abel, O., 1912, Grundzüge der Palaeobiologie der Wirbeltiere, E. Schweizerbart'sche Verlagsbuchhandlung Nägele und Dr Sproesser, Stuttgart Though this hypothesis was doubted by Nopcsa,V. Pietschinann (ed), 1914, Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien, Vienna, pp 380 it was adopted by the Danish researcher Gerhard Heilmann who in 1916 proposed that a quadrupedal Hypsilophodon lived like the modern tree-kangaroo Dendrolagus.Heilmann., G., 1916, Vor nuværende Viden om Fuglenes Afstamning, Copenhagen In 1926 Heilmann had again changed his mind, denying that the first toe was opposable because the first metatarsal was firmly connected to the second,Heilmann, Gerhard, 1926, The Origin of Birds. London, Witherby but in 1927 Abel refused to accept this.Abel, O., 1927, Lebensbilder aus der Tierwelt der Vorzeit, Fisher, Jena In this he was in 1936 supported by Swinton who claimed that even a forward pointing first metatarsal might carry a movable toe. As Swinton was a very influential populariser of dinosaurs, this remained the accepted view for over three decades, most books typically illustrating Hypsilophodon sitting on a tree branch. However, Peter M. Galton in 1969 performed a more accurate analysis of the musculo-skeletal structure, showing that the body posture was horizontal.Galton, P.M., 1969, "The pelvic musculature of the dinosaur Hypsilophodon (Reptilia : Ornithischia)", Postilla, 131: 1-64 In 1971 Galton in detail refuted Abel's arguments, showing that the first toe had been incorrectly reconstructed and that neither the curvature of the claws, nor the level of mobility of the shoulder girdle or the tail could be seen as adaptations for climbing,Galton, P.M., 1971, "Hypsilophodon, the cursorial nonarboreal dinosaur", Nature, 231: 159-161 concluding that Hypsilophodon was a bipedal running form.Galton, P.M., 1971, "The mode of life of Hypsilophodon, the supposedly arboreal ornithopod dinosaur", Lethaia, 4: 453-465 This convinced the paleontological community that Hypsilophodon remained firmly on the ground.
