Iguanodonts were herbivorous dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s that lived from the mid-Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 to Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

. Some members include Camptosaurus

Camptosaurus

Camptosaurus is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic period of western North America. The name means 'flexible lizard', ....

, 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...

, Iguanodon

Iguanodon

Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...

, Ouranosaurus

Ouranosaurus

Ouranosaurus is an unusual genus of herbivorous iguanodont dinosaur that lived during the early Cretaceous about 110 million years ago in what is now Africa. Ouranosaurus measured about seven to eight meters long...

, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found. They are among the best known of the dinosaurs, and were among the most diverse and widespread herbivorous dinosaur groups of the Cretaceous period. Iguanodontians were generally large animals, and some (such as Shantungosaurus

Shantungosaurus

Shantungosaurus, meaning "Shandong Lizard", is a genus of saurolophine hadrosaurid dinosaurs found in the Late Cretaceous Wangshi Formation of the Shandong Peninsula in China.-Description:...

, which measured up to 50 ft (15 m) in length and weighed up to 8 tons) equaled the largest carnivorous dinosaurs in size.

Classification

Iguanodontia is often listed as an infraorder within a suborder Ornithopoda, though Benton (2004) lists Ornithopoda as an infraorder and does not rank Iguanodontia. Traditionally, iguanodonts were grouped into the superfamily Iguanodontoidea and family Iguanodontidae. However, phylogenetic studies show that the traditional "iguanodontids" are a paraphyletic grade leading up to the hadrosaurs

Hadrosaurid

Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...

 (duck-billed dinosaurs). Groups like Iguanodontoidea are sometimes still used as unranked clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

s in the scientific literature, though many traditional "iguanodontids" are now included in the more inclusive group Hadrosauroidea

Hadrosauroidea

Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and their close relatives. Many primitive hadrosauroids, such as the sail-backed Ouranosaurus, have traditionally been included in a paraphyletic "Iguanodontidae"...

.

Iguanodontia is usually defined as the most inclusive group containing Parasaurolophus walkeri but not Hypsilophodon foxii or Thescelosaurus neglectus, or other combinations of species that would ultimately result in the same group in most modern analyses. The group was first defined as a clade in 2008 by Paul Sereno

Paul Sereno

Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...

.

Many iguanodonts have not yet been included in a large phylogenetic analyses, or are too fragmentary to place confidently. These include Barilium

Barilium

Barilium is a genus of iguanodontian dinosaur which was first described as a species of Iguanodon by Richard Lydekker in 1888, the specific epithet honouring the discoverer Charles Dawson....

, Bolong

Bolong

Bolong is a genus of iguanodontoid dinosaur known from the Early Cretaceous-age Yixian Formation of western Liaoning Province, China. It was named by Wu Wen-hao, Pascal Godefroit and Hu Dong-yu in 2010 and the type species is Bolong yixianensis....

, Bihariosaurus

Bihariosaurus

Bihariosaurus was a genus of camptosaurid dinosaur from Late Cretaceous Romania. The type species, Bihariosaurus bauxiticus, was described by Marinescu in 1989. It was similar to Camptosaurus, and was an iguanodont....

, Delapparentia

Delapparentia

Delapparentia is a genus of iguanodont dinosaur from the Early Cretaceous period of Galve, Teruel Province, Spain.The type specimen, MPT/I.G, was found in the Spring of 1958 by amateur palaeontologist José María Herrero Marzo...

, Dollodon

Dollodon

Dollodon is a genus of ornithopod dinosaur that lived in the Barremian and possibly the early Aptian ages of the Early Cretaceous Period of Europe. Its remains are known from Belgium , England and possibly Germany...

, Draconyx

Draconyx

Draconyx is a genus of dinosaur from the Late Jurassic. It was an ornithopod which lived in what is now Portugal. It was found in Lourinhã, in 1991, and described by Octávio Mateus and Miguel Telles Antunes in 2001.-Etymology:...

, Kukufeldia

Kukufeldia

Kukufeldia is a genus of iguanodont which existed in what is now England during the Early Cretaceous period. Identified from a nearly complete right dentary found near Cuckfield and originally described in 1848 by Gideon Mantell, it was named by Andrew T. McDonald, Paul M. Barrett, and Sandra D....

, Hypselospinus

Hypselospinus

Hypselospinus is a genus of iguanodontian dinosaur which was first described as a species of Iguanodon by Richard Lydekker in 1889, the specific name honouring William Henry Fitton....

, Macrogryphosaurus

Macrogryphosaurus

Macrogryphosaurus is a genus of basal iguanodont dinosaur from the Turonian-early Coniacian age Upper Cretaceous Portezuelo Formation of Patagonia, Argentina. It was described by Jorge Calvo and colleagues, with M...

, Owenodon

Owenodon

Owenodon is a genus of iguanodontian dinosaur known from a partial lower jaw discovered in Early Cretaceous-age rocks of Durlston Bay, Dorset, United Kingdom. The specimen, NHM R2998, comes from the Purbeck Limestone, dating to the middle Berriasian stage...

, Proplanicoxa

Proplanicoxa

Proplanicoxa is a genus of iguanodont which existed in what is now England during the Early Cretaceous period ....

, Sellacoxa

Sellacoxa

Sellacoxa is a genus of iguanodont which existed in what is now England during the Early Cretaceous period ....

and Xuwulong

Xuwulong

Xuwulong is a genus of iguanodontoid dinosaur from the Early Cretaceous period. It is a basal hadrosauriform which lived during the early Cretaceous period in what is now Yujingzi Basin in the Jiuquan area, Gansu Province of northwestern China...

. The simplified 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 an analysis by Andrew McDonald and colleagues, published in November 2010 with information from McDonald, 2011.
Cladogram after Butler et al, 2011.