page_title: Iguanodon
section_title: Description
hierarchical_section_title: Iguanodon / Description
caption_attribution_description: English: Restoration of Iguanodon bernissartensis
context_page_description: Iguanodon, named in 1825, is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Cretaceous. While many species have been classified in the genus Iguanodon, dating from the late Jurassic Period to the early Cretaceous Period of Asia, Europe, and North America, taxonomic revision in the early 21st century has defined Iguanodon to be based on one well-substantiated species: I. bernissartensis, which lived from the late Barremian to the earliest Aptian ages in Belgium, Spain, Germany, England, Portugal and possibly elsewhere in Europe, between about 126 and 122 million years ago. Iguanodon were large, bulky herbivores. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food.
  The genus was named in 1825 by English geologist Gideon Mantell but discovered by William Harding Bensted, based on fossil specimens found in England and was given the species name I. anglicus.
context_section_description: Iguanodon were bulky herbivores that could shift from bipedality to quadrupedality. The only well-supported species, I. bernissartensis, is estimated to have weighed about 3.08 tonnes (3.4 tons) on average, and measured about 10 metres (33 feet) long as an adult, with some specimens possibly as long as 13 metres (43 feet). These animals had large, tall but narrow skulls, with toothless beaks probably covered with keratin, and teeth like those of iguanas, but much larger and more closely packed.
  The arms of I. bernissartensis were long (up to 75% the length of the legs) and robust, with rather inflexible hands built so that the three central fingers could bear weight. The thumbs were conical spikes that stuck out away from the three main digits. In early restorations, the spike was placed on the animal's nose. Later fossils revealed the true nature of the thumb spikes, although their exact function is still debated. They could have been used for defense, or for foraging for food. The little finger was elongated and dextrous, and could have been used to manipulate objects. The phalangeal formula is 2-3-3-2-4, meaning that the innermost finger (phalange) has two bones, the next has three, etc. The legs were powerful, but not built for running, and each foot had three toes. The backbone and tail were supported and stiffened by ossified tendons, which were tendons that turned to bone during life (these rod-like bones are usually omitted from skeletal mounts and drawings).
  Iguanodon teeth are, as the name suggests, like those of an iguana, but larger. Unlike hadrosaurids, which had columns of replacement teeth, Iguanodon only had one replacement tooth at a time for each position. The upper jaw held up to 29 teeth per side, with none at the front of the jaw, and the lower jaw 25; the numbers differ because teeth in the lower jaw are broader than those in the upper. Because the tooth rows are deeply inset from the outside of the jaws, and because of other anatomical details, it is believed that, as with most other ornithischians, Iguanodon had some sort of cheek-like structure, muscular or non-muscular, to retain food in the mouth.
caption: Restoration showing I. bernissartensis in quadrupedal pose
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