What is "hypsilophodontia"

Hypsilophodontia is a clade of small to large bodied ornithopods that lived during the Cretaceous that were found in North America, Eurasia and Australia. Traditionally the group has included almost all bipedal bird-hipped dinosaurs other than iguanodonts, and some phylogenetic analyses found it to be a natural group, but most recent studies have found that the group is mostly paraphyletic and the taxa within represent a series leading up to Iguanodontia.