Mantellisaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Ornithopoda > Iguanodontia > Ankylopollexia > Styracosterna > Hadrosauriformes > Iguanodontidae (?)

Overview: The generic name of Mantellisaurus was first officially used in 2007, when the creature was established as a new genus by the American paleontologist Gregory S. Paul. As for the fossils used by Paul in his description, however, they’ve been known to science for far longer. In 1825, the famed English physician and paleontologist Gideon Mantell described the genus Iguanodon, based on very limited fossils. In the 1830’s, similar and far more numerous fossils were found in a quarry in Kent, later referred to as the “Maidstone specimen”, which Mantell referred to Iguanodon. Later in 1925, fossils from the Isle of Wight were described as a new species of Iguanodon – Iguanodon atherfieldensis. Prior to then, the official type specimen of the genus Iguanodon had been shifted from Mantell’s original material from the 1820’s to fossils found in Belgium, which were made up of multiple complete skeletons. This would cause a problem in later years, when scientists would realize the Belgian species of Iguanodon was an entirely different genus than that first described by Mantell, as well as from the “Maidstone specimen” or from Iguanodon atherfieldensis.

Summarizing all this confusion, because the type specimen of Iguanodon was changed, the name is now attached only to the Belgian species (Iguanodon bernissartensis). Mantellisaurus is a name for the “Maidstone specimen” and the former Iguanodon atherfieldensis, which are now recognized as the same animal. The status of Mantell’s original “Iguanodon” fossils from the 1820’s is somewhat more problematic, as the bones may lack any real distinguishing features. Mantellisaurus was still a close relative of Iguanodon, as a fellow member of the ornithopod clade Iguanodontia. Some have referred Mantellisaurus specifically to the family Iguanodontidae, alongside Iguanodon, but not all are convinced it was a true iguanodontid. Mantellisaurus tended to be both shorter in length and a lot more lightly built than Iguanodon, especially in regards to its forelimbs. Similar to Iguanodon, it had thumb spikes, though they were smaller. Mantellisaurus may’ve coexisted with Iguanodon, as its fossils are known from similar Early Cretaceous-aged geological formations across Europe. Other contemporary dinosaurs may’ve included Polacanthus, Hypsilophodon, and Neovenator.