Iguanodontia

   Iguanodontia includes the "iguanodonts" and the hadrosaurids. There are two general types of iguanodonts; small and large. Small iguanodonts, including the dryosaurids, look not too dissimilar to hypsilophodonts. Large iguanodonts, like Iguanodon, typically show quadrupedal tendencies, and sometimes have well-developed spikes for thumbs. They have robust, subrectangular skulls, with some modest flaring of the beak that becomes the "duck-bill" hadrosaurids are so known for. Many iguanodonts have lost the first toe as well. The jaws also begin to show the dental batteries and spreading ability, which in function converge with the chewing ability of mammals, that hadrosaurids have fully developed. Some have prominent extensions of the neural spines, giving them buffalo-like hump-back looks, including an unnamed taxon from Utah, and Ouranosaurus.
    The early part of the first decade of the 2000s was a time when prosauropod taxonomy went hyperactive. The second half of the decade, and into the 2010s, saw that instability descend upon Iguanodon, which detonated into a a dozen-odd genera (not all of which are necessarily valid, of course) and counting.

<--Iguanodontia
     `--+--Anabisetia
          |--Talenkauen
          `--+--Rhabdodontidae
               |    |--Rhabdodon
               |    `--+--Mochlodon
               |         `--Zalmoxes
               |--Muttaburrasaurus
               `--+--Tenontosaurus
                    `--+--Dryosauridae
                         |    |--Callovosaurus
                         |    |--Dryosaurus
                         |    |--Dysalatosaurus
                         |    |--Elrhazosaurus
                         |    `--Valdosaurus
                         `--Ankylopollexia (refers to the big ol' spiked thumbs)
                              |--Camptosauridae
                              |    `--Camptosaurus
                              `--Styracosterna
                                   |--Uteodon
                                   |--Cumnoria                                   
                                   |--Owenodon
                                   `--+--Hippodraco
                                        |--Hypselospinus
                                        |--Planicoxa
                                        |--Theiophytalia
                                        `--+--Cedrorestes
                                             |--Dakotadon
                                             |--Iguanacolossus
                                             |--Lanzhousaurus
                                             |--Osmakasaurus
                                             `--+--Kukufeldia
                                                  `--+--Barilium
                                                       |--Fukuisaurus
                                                       `--Iguanodontoidea (also Hadrosauriformes)
                                                            |--Iguanodon
                                                            |--Mantellisaurus
                                                            `--Hadrosauroidea
                                                                 |--Ouranosaurus
                                                                 `--+--Altirhinus
                                                                      |--Bolong
                                                                      |--Equijubus
                                                                      |--Lurdusaurus  
                                                                      |--Xuwulong
                                                                      `--+--+--Jinzhousaurus
                                                                           |    `--Penelopognathus
                                                                           `--+--"Probactrosaurus" mazongshanensis
                                                                                `--+--Eolambia
                                                                                     |--Jintasaurus
                                                                                     |--Probactrosaurus
                                                                                     `--+--Jeyawati
                                                                                          `--+--Protohadros
                                                                                               `--+--Levnesovia 
                                                                                                    |--Nanyangosaurus
                                                                                                    `--+--Tanius
                                                                                                         `--+--Bactrosaurus
                                                                                                              `--+--Gilmoreosaurus
                                                                                                                   `-->Hadrosauridae

Iguanodontia: Basal Iguanodontia is a home for misfits, it seems; there is the hypsilophodont-like Rhabdodon and its allies, the "iguanodontid"-like Muttaburrasaurus, and the long-tailed oddball Tenontosaurus, among others. The ordering is a bit controversial, and goes back and forth with which taxon is put at the base of Iguanodontia.

Taxon or Taxa: Time/Place: Comments:
Anabisetia saldiviai Coria and Calvo, 2002 Cenomanian-early Turonian (LK) of Argentina Anabisetia is a basal iguanodontian, based on a partial skull, parts of four cervicals, four dorsals, four sacrals, a dozen caudals, most of both shoulders and arms, and most of a leg. At least three more individuals are known, each about two meters in length. It is more derived than Gasparinisaura, which tends to show up at the "hypsil"-iguanodontian borderland.
Talenkauen santacrucensis Novas, Cambiaso, and Ambrosio, 2004 Maastrichtian (LK) of Argentina From a locality in southwestern Patagonia, Talenkauen is an iguanodontian known from a skeleton minus the tail, part of the ischia and pubes, hands, and ulnae. Probably on the order of 4 m long, it looked a lot like a dryosaurid, with an elongate neck and smallish head, but with long slender arms and a robust prepubic process. There were also thin mineralized plates along the sides of the ribcage; these probably were typically cartilaginous, and their function is unknown. Similar plates are known for several hypsilophodont-grade ornithischians.  
Muttaburrasaurus langdoni Bartholomai and Molnar, 1981 late Albian (EK) of Australia Muttaburrasaurus is one of Australia's better-known dinosaurs. Superficially, it is very much like advanced iguanodontids, but in many ways it is actually very basal, and possibly is related to the hypsilophodont Atlascopcosaurus or the rhabdodontids. It has a prominent, unusual rise on the nose, and has very odd teeth. Some researchers have suggested it was partially carnivorous.
Tenontosaurus: Ostrom, 1970 T. tillettorum (type) Ostrom, 1970 Aptian-Albian (EK) of Montana, Oklahoma, Texas, Utah, and Wyoming Long-tailed, tall-spined Tenontosaurus is known from dozens of specimens of all ages. It seems to have been a favorite food source for Deinonychus. At times classified as a hypsilophodontid, at times as an iguanodontid, it seems to be between the two. It probably was mostly quadrupedal. Other species may be found in the copious material referred to the type species.
?T. dossi Winkler, Murray, and Jacobs, 1997 late Albian (EK) of Texas T. dossi is more basal than the type, and is pretty long, on the order of 7 to 8 meters (not that the type species is any slouch). It may end up in its own genus.

Iguanodontia i.s.:  Several unnamed iguanodontians are known from the Cedar Mountain Formation, including a possible hadrosaurian. 

Taxon or Taxa: Time/Place: Comments:
Bihariosaurus bauxiticus (N.D.) Marinescu, 1989 ?Berriasian-?Hauterivian (?EK) of Romania This obscure animal is an iguanodontian, possibly close to Camptosaurus but based on scanty remains
"Cetiosaurus" brachyurus (N.D.) Owen, 1842 mid Valanginian (EK) of England This is a dubious species of Cetiosaurus named from an iguanodont dorsal and caudal (well, there wasn't much to go on yet). Which iguanodont it was will probably remain a permanent question, since you've got at least Barilium, Hypselospinus, and the original Iguanodon to choose from. 
"Gilmoreosaurus" atavus (N.D.) Nesov, 1995 late Albian (EK) of Central Asia This is an indeterminate iguanodontian ornithopod, based on teeth.
"Iguanodon": "I." anglicus (N.D.) Holl, 1829 late Valanginian (EK) of England As many of you probably know by now, the original type material for Iguanodon is pretty dodgy as these things go (some teeth), so the genus was conserved and I. bernissartensis made the type species. This leaves the teeth and postcranial bones referred to "I." anglicus in the lurch, as they aren't Bernissart Iguanodon, and nobody has really looked at them much in the last 150 years.
Additionally, there is "Iguanodon" mantelli, which also has a convoluted history. The type is actually the same as "I." anglicus, but historically was identified as the Maidstone partial skeleton (the "Mantel-piece"), from much younger (early Aptian) rocks; if only someone had named the Maidstone skeleton, we could have had an easier time of things. The Maidstone specimen probably pertains to Mantellisaurus. "I." anglicus may or may not have something to do with Kukufeldia.
"I." orientalis (N.D.) Rozhdestvensky, 1952 Aptian-Albian (EK) of Mongolia "I." orientalis is based on a maxilla, ribs, and a scapula. For a while, the skull now named Altirhinus was thought to be a specimen, but obviously no longer is. It may be a specimen of I. bernissartensis (if its name was Marco Polo, I suppose), but the scrappy remains are not notably different from those of most dinosaurs of the iguanodontian persuasion.
"I." ottigeri (N.D.) Galton and Jensen, 1979 early Aptian (EK) of Utah Based on teeth, this dubious Iguanodon species is sometimes seen named in connection with an undescribed high-spined iguanodontian from the same time and place.
Loncosaurus argentinus (N.D.) Ameghino, 1898 Santonian-early Campanian (LK) of Argentina Long misidentified due to theropod teeth mixed in with the type, this animal is some sort of ornithopod, perhaps a dryosaurid.
Macrogryphosaurus gondwanicus Calvo, Porfiri, and Novas, 2007 Turonian-early Coniacian (LK) of Argentina Macrogryphosaurus is a basal iguanodontian akin to Talenkauen (even including those odd lateral plates on the rib cage), known from postcranial remains.
Proa valdearinnoensis McDonald, Espílez, Mampel, Kirkland, and Alcalá, 2012 early Albian (EK) of Spain Proa slots in somewhere around Iguanodontoidea. It is known from cranial and postcranial remains representing multiple individuals.
Proplanicoxa galtoni (?N.D.) Carpenter and Ishida, 2010 (?Mantellisaurus) late Barremian (EK) of England Proplanicoxa is based on dorsals and a partial pelvis once referred to Vectisaurus. The name refers to Planicoxa, in recognition of features of the ilium trending like those of the earlier-named genus. Some researchers have since questioned its validity, considering it most likely a synonym of Mantellisaurus (the heir to Vectisaurus, incidentally), while Peter Galton considers it a dryosaurid, along with Osmakasaurus and Planicoxa.
Ratchasimasaurus suranareae Shibata, Jintasakul, and Azuma, 2011 Aptian (EK) of Thailand Ratchasimasaurus is known from a dentary with derived and basal characteristics.

Rhabdodontidae: Rhabdodontids were not unlike robust hypsilophodonts, with deep skulls and jaws. If you think of them at all, chances are you probably don't think of them as particularly large, but this is only partly true: although Mochlodon topped out shy of two meters long as an adult, and Zalmoxes was somewhat larger, reaching at least 2.5 meters at a subadult stage, Rhabdodon, amazingly, could reach about six meters in length.

Taxon or Taxa: Time/Place: Comments:
Rhabdodon priscus Matheron, 1869 Maastrichtian (LK) of France and Spain Rhabdodon has gone through a complicated taxonomic history. It may be found in older works under the name Mochlodon, a related animal now thought to be distinct. Rhabdodon material is fairly common, but disarticulated.
In the past, it has been regarded as an iguanodontid or a hypsilophodontid, although it now seems to be closest to animals like Tenontosaurus.
A species named R. septimanicus Buffetaut and Le Loeuff 1991 is here tentatively regarded as a synonym of the type species.
Mochlodon:
Seeley, 1881		 M. suessi (type) (Bunzel, 1871 [originally Iguanodon]) early Campanian (LK) of Austria Mochlodon and Rhabdodon were long considered the same thing, with the name varying between authorities (there was some question of nomenclatural priority involving Rhabdodon). Further research has show subtle differences between Mochlodon, Rhabdodon, and Zalmoxes.
M. vorosi Ősi, Prondvai, Butler, and Weishampel, 2012  Santonian (LK) of Hungary
Zalmoxes:
Weishampel, Jianu, Csiki, and Norman, 2003		 Z. robustus (type)  (Nopcsa, 1899 [originally Mochlodon]) early-mid Maastrichtian (LK) of Romania Zalmoxes provides a new genus for the suddenly prolific rhabdomorphs, as they are sometimes known informally. No, the name of the second species is not a typo, but if you were ever playing Paleo Scrabble, it would be a good name to remember to get rid of the "q" (heck, if you were playing some renegade version where you got a couple dozen letters, adding the genus name would probably win the game outright. Or, you could just skip the species name and use Zalmoxes.).
Z. shqiperorum Weishampel et al., 2003 early-mid Maastrichtian (LK) of Romania

Rhabdodontidae i.s.:

Taxon or Taxa: Time/Place: Comments:
Oligosaurus adelus (N.D.) Seeley, 1881 early Campanian (LK) of Austria Oligosaurus is based on a scapula, which to date has not been shown to be diagnostic.
Ornithomerus gracilis (N.D.) Seeley, 1881 early Campanian (LK) of Austria See Oligosaurus (above), except substitute "shaft of a femur" for "scapula".

Dryosauridae:  Dryosauridae is composed of several closely-knit taxa, which broadly resemble large hypsilophodonts. Annoyingly, there is a group of crocodilians known as dyrosaurids; be careful not to confuse them! An unnamed dryosaurid is present in the lower Wealden (Valanginian) of England.

Taxon or Taxa: Time/Place: Comments:

Callovosaurus leedsi Galton, 1980 (originally Camptosaurus leedsi Lydekker, 1889)

 mid Callovian (MJ) of England Once thought to be a hypsilophodont or camptosaurid, this basal iguanodontian is known from a partial femur. Its age makes it important in dating the earliest known extent of Iguanodontia.
Dryosaurus altus Marsh, 1894 (originally Laosaurus altus Marsh, 1878) Kimmeridgian (LJ) of Colorado, Utah, and Wyoming Dryosaurus is known from remains including one virtually complete skeleton, and juvenile material. Like Dysalatosaurus, its skull does not completely encircle the two nostril openings. Interestingly, adults are not yet known for either taxon.
Dysalotosaurus lettowvorbecki Virchow, 1919 late Kimmeridgian (LJ) of Tanzania Its specific name coming from a WWI German general's name, and its generic name meaning "uncatchable lizard," it seems a political message is concealed within the name. Dysalatosaurus is known from a large amount of disarticulated material. It has long been referred to approximate contemporary Dryosaurus.
Elrhazosaurus nigeriensis Galton, 2009 (originally Valdosaurus nigeriensis Galton and Taquet, 1982) late Aptian (EK) of Niger Elrhazosaurus is known from femora of the dryosaurid type.
Valdosaurus canaliculatus Galton 1977 (originally Dryosaurus canaliculatus Galton, 1975) late Barremian (EK) of England This taxon is known mostly from limb and jaw material.  What is known links it with Dryosaurus. A fair amount of material has been referred, mostly hindlimbs, hips, and skull bones. Some material suggests individuals on Mantellisaurus-scale (indeed, among material simply referred to Iguanodon may be iganodontoids, camptosaurs, and "rhabdomorphs") .

Dryosauridae i.s.:

Taxon or Taxa: Time/Place: Comments:
"Camptosaurus" valdensis (?N.D.) Lydekker, 1889 Barremian (EK) of England "Camptosaurus" valdensis is based on an ornithopod femur that has also been referred to, or suggested to belong to, Hypsilophodon (as the adult form), Valdosaurus, and a postulated genus also to include "Hypsilophodon" wielandi. It is probably the same as Valdosaurus, and for practical purposes is the same as V. canaliculatus.
Kangnasaurus coetzeei (N.D.) Haughton, 1915 EK of South Africa This is an indeterminate dryosaurid, based on teeth.  Dryosaurid postcranial material is known from the area, and may belong to it.

Camptosauridae: Camptosauridae, like Iguanodontidae, may not really exist as a monophyletic group, and tends to function best as a grade or even a state of mind; shorthand for "more derived than Dryosaurus, not as derived as Iguanodon".

Taxon or Taxa: Time/Place: Comments:
Camptosaurus dispar Marsh, 1885 (originally Camptonotus dispar Marsh, 1879) Kimmeridgian (LJ) of Colorado, Oklahoma, Utah, and Wyoming C. dispar is known from dozens of specimens.  Although often thought of as an archetypical Morrison dinosaur, it is rather rare. Also, the trademark rectangular skull actually was a composite of actual Camptosaurus material, Theiophytalia kerri's skull (thought to be from the Morrison, but actually Early Cretaceous in age), and some jiggering to get the sections to fit. New skull material gives it a more triangular, basal look, something a bit more like Dryosaurus, and with long thin palpebrals.

Camptosauridae i.s.:

Taxon or Taxa: Time/Place: Comments:
?Brachyrophus altarkansanus (N.D.) Cope, 1878 (?Camptosaurus) Kimmeridgian (LJ) of Colorado Originally considered a sauropod, Brachyrophus may well be the same animal as Camptosaurus. Interestingly, if it is, its name predates that of Camptosaurus, making it technically the senior synonym, although the fact that it has been generally ignored while Camptosaurus has become a well-known name means that it is likely any attempt to change the name will be rejected. Incidentally, the only reason I have it here, instead of Ornithischia i.s. or something like that, is because of the possibility that it is the same as Camptosaurus.
Draconyx loureiroi Mateus and Antunes, 2001 late Kimmeridgian-early Tithonian (LJ) of Portugal Recently named from the partial remains of a single individual, mostly pertaining to the limbs (best material from the hindlimbs), Draconyx belongs to the Lourinha fauna, and is related to Camptosaurus.

Styracosterna:  Because of the number of taxa, I opted to alphabetize them instead of listing them in the order they are on the diagram above.

Taxon or Taxa: Time/Place: Comments:
Barilium dawsoni Norman, 2010 (originally Iguanodon dawsoni Lydekker, 1888) (including Sellacoxa pauli Carpenter and Ishida, 2010) late Valanginian (EK) of England Barilium was a large (on the order of 10 m long) and relatively basal iguanodontian. It is known from several specimens and a fair amount of the skeleton. It had a very robust and stocky build, with small thumb spikes fused to the fused wrist bones. Teeth in jaws assigned to this taxon resemble those of Iguanodon anglicus, which was named from teeth found in the same formation. They are distinct from teeth of the contemporaneous Hypselospinus.
Included in Barilium is the pelvis and vertebrae given the name Sellacoxa pauli. Barilium may also encompass Kukufeldia tilgatensis.
Cedrorestes crichtoni Gilpin, DiCroce, and Carpenter, 2006  middle Aptian (EK) of Utah Based on a sacrum, one complete ilium and a chunk of the other, a right tibia and 3rd metatarsal, ribs, and the inescapable ossified tendons always to be found with ornithopod skeletons consisting of more than bits and pieces, Cedrorestes is a contender for oldest basal hadrosaurid. This assessment is based on features of the ilium, especially the presence of an antitrochanter (a lateral knob on the caudal portion of the ilium that hadrosaurids have but their more basal cousins lack). I'm a little wary of basing classifications on one character, and of basalmost hadrosaurids (Eolambia and Protohadros, anybody?), so I'll put it here for the time being. 
Cumnoria prestwichii Seeley, 1888 (originally Iguanodon prestwichii Hulke, 1880) Kimmeridgian (LJ) of England Cumnoria, more often known as Camptosaurus prestwichii, is quite obscure and somewhat more generalized than the more famous Morrison Formation genus, although it's got a partial skeleton and skull to its credit.
Dakotadon lakotaensis Paul, 2008 (originally Iguanodon lakotaensis Weishampel and Bjork, 1989) mid Barremian (EK) of South Dakota Dakotadon is a much better supported North American possible Iguanodon species than "I." ottigeri, albeit without the cool "high-spined iguanodont" lurking in the background. It is based on a partial skull that, like Theiophytalia, seems to speak of an intermediate point betwixt Camptosaurus and Iguanodon.
Fukuisaurus tetoriensis Kobayashi and Azuma, 2003 late Hauterivian-Barremian (EK) of Japan Having been first referred to informally back in 1990, Fukuisaurus finally joins the ranks of the described. It is based on cranial material, including a deep lower jaw, and seems to have secondarily lost the cranial flexibility of other derived ornithopods, although the distinction of this is uncertain now that it appears that ornithopod cranial flexibility was overestimated.
Hippodraco scutodens McDonald, Kirkland, DeBlieux, S. Madsen, Cavin, Milner, and Panzarin, 2010 late Barremian-early Aptian (EK) of Utah Hippodraco as presently known was a smallish gracile iguanodont (although the type individual may have been immature). It is known from a partial skull lacking the snout, and a partial skeleton including a handful of cervicals and dorsals, the sacrum, a scapula, sternal element, and humerus, an ischial fragment, part of a femur and tibia, and most of a foot and ankle. It was found with caudals from a larger iguanodont and the scapula of a hypsil-type animal.
Hypselospinus fittoni Norman, 2010 (originally Iguanodon fittoni Lydekker, 1889) late Valanginian (EK) of England Hypselospinus, a contemporary of Barilium, was smaller and less robust, with tall slender neural spines and flat pointed thumb spikes (although note that Hypselospinus was not exactly a delicate flower itself, and Barilium had respectable neural spines of its own, but as typical for that genus they look as thought they were built to withstand significant explosions). Included is Iguanodon hollingtoniensis, known from much of a skeleton.
Iguanacolossus fortis McDonald, Kirkland, DeBlieux, S. Madsen, Cavin, Milner, and Panzarin, 2010 Barremian (EK) of Utah As its name would suggest, Iguanacolossus fortis was a large, robust iguanodont. It is thought to have been on par with Iguanodon bernissartensis in size. It is known from a partial associated skeleton mostly consisting of vertebrae, ribs, chevrons, and girdle bones, with a few skull fragments and leg bones.
Kukufeldia tilgatensis McDonald, Barrett, and Chapman, 2010 (?Barilium) late Valanginian (EK) of England Kukufeldia is a new name for an old (1848) dentary previously assigned to Iguanodon anglicus. Given the problems with I. anglicus, the authors thought it best to give the bone a different name. There is a good chance that the jaw is another example of Barilium, though.
Lanzhousaurus magnidens You, H., Q. Ji, and D. Li, 2005 EK of China As others have noticed, a Google search of Lanzhousaurus brings up a picture of a skeletal mount of a big ornithopod, certainly iguanodont-grade, as revealed by its astonishingly huge teeth (hadrosaurids have much smaller teeth). The mount is misleading, as only a lower jaw, teeth, some cervicals and dorsals, ribs, sternal elements, and both pubic bones are known. From what is known, a hadrosaurid length (~10 m, 33 ft) is suggested; a rather tubby mass of 5.5 metric tons is also suggested, which seems off given that most hadrosaurids of the same length are thought to have massed more like 2-3 metric tons.
Osmakasaurus depressus McDonald, 2011 (originally Camptosaurus depressus Gilmore, 1909) Barremian (EK) of South Dakota Osmakasaurus spent the first century of its scientific life as Camptosaurus depressus, the species of Camptosaurus that no one ever talked about (it seems that no one ever talks about C. prestwichii [Cumnoria], either, but it at least has the "English camptosaur" point in its favor). It is more similar to Planicoxa in the low depressed form of its ilium than it is to Camptosaurus, and was once assigned to that genus as P. depressa. It is known only from the same site as the type specimen of Hoplitosaurus. It has been mooted as a possible dryosaur.
Owenodon hoggii Galton, 2009 (originally Iguanodon hoggii Owen, 1874) mid Berriasian (EK) of England For a long time considered to be the earliest occurrence of Iguanodon, and then more recently thought to pertain to Camptosaurus, Owenodon appears to be somewhere between Camptosaurus and Lurdusaurus. It is based on a dentary. More material would be very helpful. Similar teeth are known from Spain and Romania.
Planicoxa venenica
DiCroce and Carpenter, 2001		 mid Aptian (EK) of Utah A new Cedar Mountain Formation iguanodontian, Planicoxa (with its interesting name, to me reminiscent of a plant) is known from an ilium, vertebrae, and partial fore and hindlimbs, belonging to at least two individuals. Like the other "planicoxic" iguanodonts (Proplanicoxa and Osmakasaurus, at one point thought to be a second species of Planicoxa), Galton considers it to be a dryosaurid.
Theiophytalia kerri Brill and Carpenter, 2006 Aptian-Albian (EK) of Colorado The so-called "Garden of the Gods" iguanodont, Theiophytalia is based on a partial skull (muzzle, cheek, and caudal half of the lower jaw, essentially) that seems akin to Dakotadon and somewhere between Camptosaurus (which it used to stand in for, until it was realized that the skull wasn't from the Morrison but from younger rocks) and Iguanodon.
Uteodon aphanoecetes McDonald, 2011 (originally Camptosaurus aphanoecetes Carpenter and Y. Wilson, 2008) Tithonian (LJ) of Utah With the 2006 publication of a Camptosaurus skull that contained less than 50% accidentally reprocessed Theiophytalia, and the concurrent renovation of the Carnegie's dinosaur exhibits, the Dinosaur National Monument specimens of Camptosaurus were reevaluated by Carpenter and Wilson and found to differ from C. dispar in a variety of proportions. They gave the material the new species name C. aphanoecetes, later to become its own genus, Uteodon. 

Taxa That Are Probably the Same as Iguanodon or Mantellisaurus, But Haven't Been Dealt With Much, or: Victorian Iguanodont Taxa You've Probably Never Heard Of: The first decade of the 21st century has seen what we used to call Iguanodon spun off into numerous genera, which is by and large a good thing. However, it has also left a bunch of former Iguanodon synonyms without a comfortable place of address. This is most obvious with the "gracile iguanodont" now called Mantellisaurus atherfieldensis. Several goes were made at naming gracile iguanodonts, including I. mantelli (Meyer, 1832; a misinterpretation, as the name seems to have been based on the same material as I. anglicus, but became used for the gracile Bernissart iguanodont), Heterosaurus neocomiensis (Cornuel, 1850), Sphenospondylus gracilis (Lydekker, 1888), and Vectisaurus valdensis (Hulke, 1879); Iguanodon atherfieldensis just happened to be based on the best material, and the others were lumped in with it. However, as you can see below, several of the others derive from different areas and different time periods, so there could well be a situation where, say, Heterosaurus, Mantellisaurus, and Vectisaurus are distinct taxa (if of course they are all based on diagnostic material).

Taxon or Taxa: Time/Place: Comments:
Heterosaurus neocomiensis (?N.D.) Cornuel, 1850 early Hauterivian (EK) of France Heterosaurus is based on a partial Mantellisaurus-like iguanodont skeleton (and some plesiosaur and ichthyosaur material thrown in for good measure, hence the name meaning "different tooth"). The remains are supposedly not bad (both for the iguanodont and the marine reptiles), which combined with the age make it a worthy topic of restudy. It would be interesting to see what ends up with the name (Heterosaurus being implicated in the whole Mantellisaurus ball of wax, although it seems a bit old, geologically speaking, to be a real threat).
Sphenospondylus gracilis (N.D.) Lydekker, 1888 Barremian to/or Aptian (EK) of England Sphenospondylus is a dubious iguanodontian based on dorsal vertebrae from the Isle of Wight.
Vectisaurus valdensis (?N.D.) Hulke, 1879 late Barremian (EK) of England Vectisaurus is the most well-known of the "gracile iguanodont" names that were beaten out by Mantellisaurus; its use persisted into the 1980s, and it was noted for its high spines. The high spines were once thought to differentiate Vectisaurus from what is now called Mantellisaurus, but they both had tall spines. Interestingly, Vectisaurus comes from older rocks than indisputable Mantellisaurus. It is based on a handful of vertebral centra and other vertebral fragments, and a partial ilium.

Iguanodontoidea and Hadrosauroidea: So, what's the difference between Iguanodontoidea and Hadrosauroidea?  The definition for Hadrosauroidea is written to specifically exclude Iguanodon bernissartensis, while that of Iguanodontoidea is written to include it. Why do I have both in the diagram?  When I started, I was using Iguanodontoidea, but by the end of the first decade of the 2000s Hadrosauroidea had entered wider usage. Hadrosauriformes is the same thing as Iguanodontoidea, just without a potentially-misleading suffix (all of these "-oideas").
    Many of these basal hadrosauroids were once classified as iguanodontids, but while they are similar to Iguanodon, they are not in the same family; rather, they are part of the line that ends up as hadrosaurids. Many derived hadrosauroids outside of the hadrosaurids (i.e. Bactrosaurus) were once classified as hadrosaurids, but have since been pushed out of that club.
    As with Styracosterna, I have opted to alphabetize.

Taxon or Taxa: Time/Place: Comments:
Altirhinus kurzanovi Norman, 1998 late Aptian-early Albian (EK) of Mongolia Based on material once referred to the now-defunct taxon Iguanodon orientalis, this hadrosauroid had a prominent nasal arch.
Bactrosaurus johnsoni Gilmore, 1933 early Maastrichtian (LK) of China Bactrosaurus is pretty close to the dividing line between hadrosaurids and their more basal cousins, and is often described as a basal hadrosaurid. It is known from partial skeletons belonging to robust individuals. According to the common interpretation, at the time of describing an iguanodont-like skull got mixed in with the remains and made an animal with a classic lambeosaurine postcranium into a saurolophine. Later, it was discovered that two hadrosaurids were represented in the remains, one being the lambeosaurine Bactrosaurus, the other (and the owner of the skull) a saurolophine-like animal now named Gilmoreosaurus. However, some researchers are suggesting, based on further bonebed material, that Bactrosaurus was not chimeric and the flat skull actually a part of one individual (but still separated from Gilmoreosaurus), making this animal not a lambeosaurine, but a more basal hadrosauroid.
Bolong yixianensis Wu W.-H., Godefroit, and Hu D.-Y., 2010 early Aptian (EK) of China As its species name makes clear, Bolong is a Yixian iguanodont, described as a basal iguanodontoid. It is known from a partially complete skeleton. It was a fairly small iguanodont (~4 m length), with short robust forearms and shins.
Eolambia caroljonesa Kirkland, 1998 latest Albian-earliest Cenomanian (EK-LK) of Utah Once thought as to be the earliest known hadrosaurid (but not the most generalized-Protohadros had that honor), this was originally going to be called "Eohadrosaurus caroljonesi" before its supposed lambeosaurine affinities were clear (more recent work suggests it is a more basal iguanodontian). Several individuals are known, and their remains make up most of a skeleton.
Equijubus normani You, Luo, Shubin, Witmer, Tang Z., and Tang F., 2003 Aptian-Albian (EK) of China Very little has yet been revealed on this possible basal "hadrosaurian". A short-snouted skull and partial postcranial remains are known. It is said to be similar to Altirhinus and Jinzhousaurus.
Gilmoreosaurus mongoliensis Brett-Surman, 1979 (originally Mandschurosaurus mongoliensis Gilmore, 1933) early Maastrichtian (LK) of China Gilmoreosaurus was long confused with the dubious hadrosaurid Mandschurosaurus. Some material once referred to Bactrosaurus appears to actually belong to the contemporaneous Gilmoreosaurus instead, which has a more gracile body.
Iguanodon bernissartensis Mantell, 1825 (type species after Boulenger vide Van Beneden, 1881) Barremian-early Aptian (EK) of Belgium, England, France, Germany, and Spain Iguanodon was one of the three founding members of Sir Richard Owen's Dinosauria. By now, though, that original material is no longer known as Iguanodon.
Originally, it was restored somewhat like the iguana it was named for, as a giant lizard with a horn on its nose (which turned out to be a thumb spike). Then, after the Belgian finds of the late 1800s, a tripodal kangaroo-like posture came to be favored. Finally, it has become a quadruped since about the 1980s, most notably in Disney's Dinosaur.
Although Iguanodon gets the fame for being a founding member, the original type material was pretty poor (teeth, if your memory serves you well), and given the potential for taxonomic weirdness, the name was recently shifted to a specimen of I. bernissartensis. Just to illustrate that noting is ever as simple as it seems, I. bernissartensis itself was technically named in a critique of an unpublished paper.
I. bernissartensis is known from 26 skeletons and much partial and isolated material, including the famous Bernissart quarry, where at least 32 individuals were found. It is much more robust than Mantellisaurus, with long massive forelimbs (and a hadrosaurid-length body of 10 to up to 13 meters), while Mantellisaurus was much shorter, at around 6 to 7 meters in length, and likely a lower browser. Iguanodon is more common in Belgium, with Mantellisaurus the rare local gracile genus, but the gracile Mantellisaurus is more common in England.
It has occasionally been suggested that Mantellisaurus and I. bernissartensis are the two sexes of one species, but this now appears to be an untenable position.
Iguanodon seelyi Hulke 1882, here considered a probable synonym of I. bernissartensis is based upon a right leg, right humerus, left ilium, left pes, caudals, and chevrons, from the Isle of Wight. The name is often given as seeleyi, probably on the assumption it is named after Harry Seeley, but it is actually named after a C. Seely who permitted excavation. It was mixed up with Dollodon briefly, even inspiring the new combination Dollodon seelyi, but the similarities were overstated, and I. seelyi is a good exemplar of a robust iguanodont, being in fact larger and more robust than I. bernissartensis itself.
Jeyawati rugoculus McDonald, Wolfe, and Kirkland, 2010 middle Turonian (LK) of New Mexico  Jeyawati is a hadrosauroid that falls out somewhere between the "near-hadrosaurs" Probactrosaurus, Eolambia, and Protohadros, and the traditional "base of Hadrosauridae" characters Bactrosaurus, Telmatosaurus, and friends. It is known from a partial skull and skeleton, with the most obvious distinguishing feature being its knobbly postorbitals.
Jintasaurus meniscus You H. and Li D., 2009 Aptian-Albian (EK) of China Jintasaurus is known from a partial posterior skull from a derived non-hadrosaurid iguanodont, but there seems to be something odd going on with the definitions used in the description. It was described as the sister group to Hadrosauroidea, but that doesn't make sense: Hadrosauroidea is defined as all iguanodonts closer to Parasaurolophus than Iguanodon, which would kind of make Iguanodon the default sister group of Hadrosauroidea. It is also supposed to be more derived than other EK hadrosauriforms, but again by definition, the only hadrosauriform that is not a hadrosauroid is Iguanodon. This leaves me somewhat puzzled, but if you consider it as more derived than Protohadros, as the authors did, that at least puts you into familiar real estate.
Jinzhousaurus yangi Wang and Xu, 2001 early Aptian (EK) of China A Yixian dinosaur, although not from the same level that has produced so many feathered finds, Jinzhousaurus is a large (~7 m long) iguanodontian based on material including an almost complete skeleton and skull that show an odd mix of basal and derived characters. It apparently is not as close to hadrosaurids as Probactrosaurus.
Levnesovia transoxiana Sues and Averianov, 2009 middle-late Turonian (LK) of Uzbekistan One man's hadrosauroid is another man's basal hadrosaurid, depending on how the definitions are worked. Levnesovia was described as a basal hadrosauroid related to Bactrosaurus which, for the purposes of this site, puts it in Hadrosauridae. The two, possibly with Gilmoreosaurus, may represent an early radiation of hadrosaurids/oids. Material including cranial and vertebral fossils is known to date.
Lurdusaurus arenatus Taquet and Russell, 1999 late Aptian (EK) of Niger Having long gone under the informal name "Gravisaurus tenerensis" (Chabli, 1988), this animal was one of the most heavily-built iguanodontians. It has been compared to prehistoric giant ground sloths.
Remains of two individuals of this unusual iguanodontian are known. It may have gotten to be around 9 meters long, with short hindlimbs and stout forelimbs armed with enlarged thumb spikes, making their arms like maces. 
Mantellisaurus atherfieldensis Paul, 2006 (originally Iguanodon atherfieldensis Hooley, 1924) (including Dollodon bambingi Paul, 2008) Barremian-early Aptian (EK) of Belgium and England To continue from above: this is one iteration of the "gracile (skinny, slim, fine-boned, what-have-you) Iguanodon". Although I. atherfieldensis needs its own generic name, as noted above precisely which name to use is a frustrating matter: literally, it is the youngest of several probable synonyms, which is not supposed to happen. We'll see how that flies in the next few years (this must be like waiting for someone to challenge the constitutionality of a law), but Mantellisaurus is a good start.
Paul introduced the name Dollodon bampingi for the gracile Bernissart iguanodont, long known as I. mantelli or I. atherfieldensis. It has also been combined with "Iguanodon" seelyi Hulke, 1882, from the Barremian of England, as Dollodon seelyi, but that species is probably a synonym of I. bernissartensis. Dollodon probably represents a nearly mature Mantellisaurus, compared to a partially grown type.
Nanyangosaurus zhugeii Xu, Zhao, Lu, Huang, Li, and Dong, 2000 ?Albian (EK) of China This animal, based on a partial postcranial skeleton, appears to be just basal to the true hadrosaurids (or just on the other side of that "line").
Ouranosaurus nigeriensis Taquet, 1976 late Aptian (EK) of Niger Ouranosaurus is most famous for its well-developed ridge-back, much like that of some spinosaurids. It had a sort of knob right in front of the eyes. A couple of good skeletons are known.
Penelopognathus weishampeli Godefroit, Li, and Shang, 2005 Albian (EK) of Mongolia This hadrosauroid, based on a long, low right dentary (most hadrosauroids tend to have short, robust lower jaws), may be more derived than Altirhinus but less than Probactrosaurus based on dental characters.
Probactrosaurus gobiensis Rozhdestvensky, 1966 (including P. alashanicus Rozhdestvensky, 1966) Barremian-Aptian (EK) of China Probactrosaurus is the sort of animal that would be expected as the ancestor of the hadrosaurids (made explicit in the name: "before Bactrosaurus"), if the material has been interpreted correctly. It has a plain iguanodont skull, without crests or knobs.
"Probactrosaurus" mazongshanensis Lu, 1997 Barremian (EK) of China Based on fragmentary remains, this species seems to be closer to Altirhinus than to Probactrosaurus.
Protohadros byrdi Head, 1998 Cenomanian (LK) of Texas This recently-described dinosaur, based on a skull and some postcranial bits, was first described as the most basal hadrosaurid yet discovered, but it now appears to be a derived non-hadrosaurid iguanodontian. It has an unusually large lower jaw.
Tanius sinensis Wiman, 1929 early-mid Maastrichtian (LK) of China Considered at times to be congeneric with Tsintaosaurus, this obscure and mysterious hadrosauroid is known from ?three disarticulated specimens. At times it has been classified as a basal hadrosaurid, although it may have lambeosaurine affinities.
Xuwulong yueluni You H., Li D., and Liu W., 2011 Aptian-Albian (EK) of China Xuwulong is a basal hadrosauroid, known from a partial articulated skeleton including a skull, most of the vertebral column (minus part of the tail), ribs and chevrons, and the left pelvis. It may be close to Equijubus.

Hadrosauroidea i.s.:

Taxon or Taxa: Time/Place: Comments:
"Bactrosaurus" prynadai (N.D.) Riabinin, 1939 Coniacian-Santonian (LK) of Kazakhstan Your run-of-the-mill obscure indeterminate hadrosauroid, known from parts of the lower and upper jaws.
Batyrosaurus rozhdestvenskyi Godefroit, Escuillié, Bolotsky, and Lauters, 2012 Santonian-Campanian (LK) of Kazakhstan Batyrosaurus is known from a partial skull and pectoral/arm material (sternals, humerus, radius, metacarpals, and phalanges). It is a basal-ish hadrosauroid (think Altirhinus, Eolambia, or Probactrosaurus).
"Cionodon" kysylkumensis (N.D.) Riabinin, 1931 upper Turonian-Coniacian (LK) of Uzbekistan This animal may be some sort of basal hadrosaur. It is known from a partial maxilla (mistaken for a dentary), verts, and a tibia.
Delapparentia turolensis Ruiz-Omeñaca, 2011 early Barremian (EK) of Spain Delapparentia is based on material formerly assigned to Iguanodon bernissartensis, and like that taxon was a generous serving of iguanodont, on the order of 10 m long. It is known from a fragmentary partial skeleton including cervical and caudal verts, fragments of dorsal and sacrals, fragments of ribs, chevrons, and ossified tendons, and a partial left hip. The caudal neural spines were fairly tall. Interestingly enough, there is also an unnamed iguanodont with tall neural spines on its dorsals, found in contemporary to slightly older rocks in Spain, though we shouldn't read too much into this yet given that tall neural spines are hardly a rarity among iguanodonts. 
"Gilmoreosaurus" arkhangelskyi (?N.D.) Nesov, 1995 late Turonian-Coniacian (LK) of Uzbekistan G. arkhangelski is known from isolated bones of multiple types of iguanodonts, one of which may be Levnesovia.
Huehuecanauhtlus tiquichensis Ramírez-Velasco, Benammi, Prieto-Márquez, Ortega, and Hernández-Rivera, 2012 Santonian (LK) of Mexico Making a bold splash into the pool of dinosaur names that would make demoralizing selections for a spelling bee, Huehuecanauhtlus was a derived non-hadrosaurid hadrosauroid. It is known from fossils including jaw, pelvic, and vertebral remains.
"Iguanodon" hilli (N.D.) Newton, 1892 Cenomanian (LK) of England A rare European hadrosauroid, this is also one of the earliest known hadrosauroids. It is known from a tooth.
"Mandschurosaurus" laosensis (N.D.) Hoffet, 1943 Aptian-Albian (EK) of Laos This obscure iguanodont is known from fragmentary postcranial remains including at least an ilium. It was getting by as a hadrosaurid on the basis of a purported late LK age.
Siamodon nimngami Buffetaut and Suteethorn, 2011 Aptian (EK) of Thailand Described as a Probactrosaurus-grade iguanodont, Siamodon is known from a maxilla, braincase, and tooth.
"Trachodon" cantabrigiensis (N.D.) Lydekker, 1888 late Albian (EK) of England This is a very early indeterminate hadrosauroid, mostly known for popping up in discussions of early hadrosaurids as a possible example.

Hadrosauridae:  Hadrosauridae is the group comprising the "duck-bills."  It also is swamped in names given to indeterminate remains.

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