Hypsilophodontidae

Hypsilophodonts Temporal range: Early Cretaceous, 130–125 Ma PreЄ Є O S D C P T J K Pg N ↓
Hypsilophodon
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	†Ornithischia
Suborder:	†Ornithopoda
Clade:	†Hypsilophodontia
Family:	†Hypsilophodontidae Dollo, 1882
Genera
Hypsilophodon

Hypsilophodonts (named after Hypsilophodon, itself derived from the Hypsilophus ("high-crested") genus of iguana lizard and literally meaning "Hypsilophus-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, New Zealand, 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 more 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, such as Agilisaurus and Othnielosaurus (=Othnielia). Thus, the only certain member at this time is Hypsilophodon.

The following cladogram of hypsilophodont relationships depicts the paraphyletic hypotheses; the "natural Hypsilophodontidae" hypothesis has been falling out of favor since the mid-late 1990s. It is after Brown et al. (2013), the most recent analysis of hypsilophodonts. Ornithischia, Ornithopoda, and Iguanodontia were not designated in their result, and so are left out here. Additional ornithopods beyond Tenontosaurus are omitted. Dinosaurs traditionally described as hypsilophodonts are found from Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura.