Belongs within: Genasauria.
Contains: Euiguanodontia.
The Ornithopoda are a clade of bipedal and facultatively quadrupedal herbivorous dinosaurs that have been defined as including all taxa closer to Iguanodon bernissartensis than to Triceratops horridus or Pachycephalosaurus wyomingensis (Fonseca et al. 2024). The composition of this clade is currently subject to revision; recent phylogenetic analyses have found that several taxa previously regarded as basal Ornithopoda should be placed outside the Ornithopoda + Marginocephalia clade. Fonseca et al. (2024) identified Ornithopoda as having the jugal well above the quadrate condyles, a lowered mandibular glenoid, no primary labial swelling on the dentary teeth, and curved dentary tooth roots. One of the best known basal ornithopods is Hypsilophodon foxii from the Early Cretaceous of England, a lightly built bipedal form less than two metres in length. Hypsilophodon forms a clade Hypsilophodontidae with the similar Gideonmantellia amosanjuanae from Spain (Fonseca et al. 2024).
Ornithopods excluding Hypsilophodontidae are included the Iguanodontia, defined as the smallest clade including Dryosaurus altus, Iguanodon bernissartensis, Rhabdodon priscus and Tenontosaurus tilletti but not Hypsilophodon foxii (Fonseca et al. 2024).
<==Ornithopoda [Euornithopoda, Hypsilophodontia]
| i. s.: Eucercosaurus tanyspondylus Seeley 1879 (n. d.)FR24, VMW04
|--Iguanodontia [Clypeodonta, Iguanodontidae]FR24
| | i. s.: AlbisaurusN04
| | |--A. albinus (n. d.)FR24
| | `--A. scutifer Fritsch 1905 (n. d.)N04
| | Loncosaurus argentinus Ameghino 1899 (n. d.)N04, FR24
| | Tichosteus (n. d.)N04
| | |--T. aequifacies Cope 1878 (n. d.)FR24
| | `--T. lucasanus Cope 1877 (n. d.)N04
| |--RhabdodontomorphaFR24
| | | i. s.: Ampelognathus coheni Tykoski et al. 2023FR24
| | |--Tenontosauridae [Tenontosaurinae]FR24
| | | |--Convolosaurus marriFR24
| | | `--+--Iani smithiFR24
| | | `--Tenontosaurus Ostrom 1970FR24, N04
| | | |--T. dossi Winkler, Murry & Jacobs 1997N04
| | | `--T. tilletti Ostrom 1970N04
| | `--RhabdodontoideaFR24
| | |--Transylvanosaurus platycephalusFR24
| | `--+--‘Rhabdodon’ septimanicus Buffetaut & le Loeuff 1991FR24, N04
| | `--+--Mochlodon Seeley 1881FR24, N04
| | | |--M. suessi (Bunzel 1871)FR24, N04 [=Iguanodon suessiN04]
| | | `--M. vorosiFR24
| | `--RhabdodontidaeFR24
| | |--Rhabdodon Matheron 1869FR24, N04
| | | `--R. priscus Matheron 1869 (see below for synonymy)N04
| | `--+--Matheronodon provincialisFR24
| | `--Zalmoxes Weishampel, Jianu et al. 2003FR24, N04
| | |--*Z. robustus (Nopcsa 1902)WJ03 (see below for synonymy)
| | `--Z. shqiperorum Weishampel, Jianu et al. 2003N04
| `--EuiguanodontiaFR24
`--HypsilophodontidaeFR24
|--Gideonmantellia amosanjuanaeFR24
`--Hypsilophodon Huxley 1869FR24, NS04
|--H. foxii Huxley 1869NS04 [=Iguanodon foxiiN85]
`--H. wielandi Galton & Jensen 1978 (n. d.)FR24
Rhabdodon priscus Matheron 1869 [incl. Oligomerus adelus Seeley 1881, Ornithomerus gracilis Seeley 1881]N04
*Zalmoxes robustus (Nopcsa 1902)WJ03 [=Mochlodon robustusN04, Mochlodon robustumWJ03, Rhabdodon robustusWJ03; incl. Onychosaurus hungaricus Nopcsa 1902N04, Camptosaurus inkeyi Nopcsa 1900N04]
*Type species of generic name indicated
References
[FR24] Fonseca, A. O., I. J. Reid, A. Venner, R. J. Duncan, M. S. Garcia & R. T. Müller. 2024. A comprehensive phylogenetic analysis on early ornithischian evolution. Journal of Systematic Palaeontology 22 (1): 2346577.
[N85] Norman, D. 1985. The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.
[N04] Norman, D. B. 2004. Basal Iguanodontia. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 413–437. University of California Press: Berkeley.
[NS04] Norman, D. B., H.-D. Sues, L. M. Witmer & R. A. Coria. 2004. Basal Ornithopoda. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 393–412. University of California Press: Berkeley.
[WJ03] Weishampel, D. B., C.-M. Jianu, Z. Csiki & D. B. Norman. 2003. Osteology and phylogeny of Zalmoxes (n. g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania. Journal of Systematic Palaeontology 1: 65–123.