Dryosaurids were primitive iguanodont

Iguanodont

Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...

s. They are known from Middle Jurassic

Middle Jurassic

The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....

 to Early Cretaceous

Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...

 rocks of Africa, Europe, and North America.

Phylogeny

Until recently many dryosaurids have been regarded as dubious

Nomen dubium

In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...

 (Callovosaurus

Callovosaurus

Callovosaurus is a genus of iguanodontian dinosaur known from most of a left thigh bone discovered in Middle Jurassic-age rocks of England. At times, it has been considered dubious or a valid genus of basal iguanodontian, perhaps a dryosaurid.-History and description:Callovosaurus is based on...

and Kangnasaurus

Kangnasaurus

Kangnasaurus is a genus of iguanodontian ornithopod dinosaur found in supposedly Early Cretaceous rocks of South Africa. It is known from a tooth and possibly some postcranial remains. At times, it has been considered dubious or a valid genus...

) or as species of the type member, Dryosaurus

Dryosaurus

Dryosaurus is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont . Fossils have been found in the western United States, and were first discovered in the late 19th century...

(Dysalotosaurus

Dysalotosaurus

Dysalotosaurus is a genus of herbivorous iguanodontian dinosaur. It was a dryosaurid iguanodontian, and its fossils have been found in late Kimmeridgian age-rocks of the Tendaguru Formation, Tanzania. The type species of Dysalotosaurus is D. lettowvorbecki. Dysalotosaurus was named by Virchow in...

, Elrhazosaurus

Elrhazosaurus

Elrhazosaurus is a genus of basal iguanodontian dinosaur, known from isolated bones found in Lower Cretaceous rocks of Niger. These bones were initially thought to belong to a species of the related dryosaurid Valdosaurus, but have since been reclassified.-Discovery and history:Elrhazosaurus is...

and Valdosaurus

Valdosaurus

Valdosaurus is a genus of bipedal herbivorous iguanodont ornithopod dinosaur found on the Isle of Wight and elsewhere in England. It lived during the Early Cretaceous.-Discovery and naming:...

). However, more recent studies redescribe these genera as valid. The cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 below follows Paul M. Barrett, Richard J. Butler, Richard J. Twitchett and Stephen Hutt (2011).