Hypsilophodontidae

Hypsilophodonts (named after the Hypsilophus genus of iguana lizard, literally meaning "high-crested tooth") were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1-2 meters long (3.3-6.6 feet). They are known from Asia, Australia, Europe, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age. The group traditionally has included almost all bipedal bird-hipped dinosaurs other than iguanodonts, and some early phylogenetic analyses found it to be a natural group, but recent studies have found that the group is mostly paraphyletic and the taxa within represent a series leading up to Iguanodontia. Some of these studies have moved some traditional hypsilophodonts out of the Ornithopoda. Thus, the only certain member at this time is Hypsilophodon. This area of the dinosaur family tree is complicated by a lack of research.