IGUANODON

Every once in a while, a palaeontologist will reconstruct a dinosaur in the image of what they genuinely believe the creature looked like and get it horribly wrong. For example, the first Iguanodon was put together like a giant four-legged Iguana with what turned out to be a huge thumb spike stuck on the end of its nose. Gideon Mantell also thought it sported some features in common with the extinct ground sloth Mylodon, had a long food-grasping tongue like a giraffe and was almost 60 feet long, which would dwarf all known carnivorous theropods and many members of Sauropoda: a great lineage of plant-eating dinosaurs that gave rise to the biggest land-dwellers in Earth's history. Alas, Iguanodon was nowhere near that size. Nor are those the last of the misconceptions that shroud it.

Mantell was an English country doctor with a passion for fossils, but it was his spouse who put Cuckfield on the map when she discovered a strange tooth amongst a pile of roadside stones as she tagged along on a house call in 1822. Although a romantic notion, rumour has it Mary Ann never went "on call" with her husband, and Mantell — perhaps wounded by the fact that his wife had deserted him and their children — later claimed to have found the fossil himself, despite initially stating otherwise. Regardless of who found it, the tooth was dismissed by the times' finest palaeontologists as belonging to a fish or rhinoceros, but when Samuel Stutchbury of the Royal College of Surgeons noticed that, size notwithstanding, it bore a striking similarity to those of modern Iguanas and William Conybeare talked Mantell out of Iguanosaurus in favour of Iguanodon in 1825, it became the second named dinosaur behind Richard Owen's Megalosaurus. Four years later, Iguanodon was honoured as the first dinosaur to receive a full binomen when Friedrich Holl attached it to the epithet anglicum (amended to anglicus in 1850 by German naturalist Heinrich Georg Bronn), and along with Hylaeosaurus and Megalosaurus, it formed the foundation on which Owen built his Dinosauria in 1842.

Over the course of the next 100 years, a mind-boggling number of specimens were assigned as species to Iguanodon, to the point where all of your fingers and toes wouldn't be enough to count them. However, a cull began towards the end of the 19th century, starting with Iguanodon suessi and Iguanodon prestwichii, which became Mochlodon and Cumnoria respectively, followed by Iguanodon exogyrarum (Procerosaurus) and Iguanodon albinus (Albisaurus) in 1905, and bits of a juvenile Iguanodon anglicus that became Valdosaurus in 1977. The trend continued into the next millennium. Gone are Iguanodon hoggi, dawsoni, fittoni, hollingtoniensis, mantelli and atherfieldensis, spirited away to become Owenodon, Barilium, Hypselospinus, Huxleysaurus, Dollodon and Mantellisaurus. Most importantly, however, gone is the name-bearer Iguanodon anglicus, the one that started it all, and what was once the quintessential English herbivorous dinosaur is now — along with the best bier, best chocolate, best detective and best tapestry — an export of the Kingdom of Belgium.

The remains of Mantell's original Iguanodon were lousy, truth be told, so in 1998, a petition was filed to the ICZN to transfer name-bearing rights to Iguanodon bernissartensis, which is what most Iguanodon research was based on anyway. The request was approved in 2000, and so Iguanodon was attached to the beautifully preserved skeletons from a Bernissart coal pit. Iguanodon anglicus, in the meantime, was placed in its own genus, Therosaurus, which was coined in 1840 by Leopold Joseph Fitzinger, kind of. Strictly speaking, Fitzinger didn't actually rename Iguanodon anglicus. He renamed Iguanodon mantelli which was coined by Christian Erich Hermann von Meyer (who ignored Holl's work and added his own epithet) for the very same tooth in 1832! Thus, Mantell's original Iguanodon is now attached to a pointless name that replaced a pointless name. Funnily enough, Friedrich von Huene named a genus of "mammal-like reptile" Therosaurus watsoni in 1925, so Therosaurus nnée Iguanodon would have had to be renamed again if Romer and Price hadn't sunk von Huene's Therosaurus as a junior synonym of Ophiacodon retroversa in 1940.

In the late 2000s and early 2010s, palaeontologists continued to smash what were previously species of Iguanodon into multiple genera, moving erroneously-assigned parts of already renamed species to new critters such as Delapparentia, Darwinsaurus, Mantellodon, and Kukufeldia. Asia got in on the act with their Iguanodon orientalis whose distinctive arched snout was renamed Altirhinus kurzanovi, and Iguanodon was also recorded from North America on the basis of two species: Utah's Iguanodon ottingeri and Iguanodon lakotaensis from South Dakota. However, the former has since been discredited as a nomen dubium while the latter is now called Dakotadon, which means Iguanodon bernissartensis (including remains that were once known as Iguanodon seelyi) is the only species of Iguanodon that is universally accepted as valid.

Iguanodon was a rustic chap, well made at around 5 tons in weight and over 12 meters in length. It has the swiss army hands; its thumbs are adorned with a massive claw for self-defence, its pinkies are supple and able to manipulate objects such as food and the three digits in between are tightly grouped and hoof-ended for weight-bearing. It had a robust, tall but narrow skull with teeth deeply inset from the outer margin of its jaws, suggesting it could retain food with cheek-like structures as it chewed in a manner not dissimilar to cows, which was quite an advanced feature for its time. The front of its jaws lacked teeth but sported a series of bony nodes that anchored a keratinous "beak" for cropping vegetation, and it walked primarily on two legs but had no problems switching to four-leg drive.