structural:expansion, structural:reformatting
21st century research and the splitting of the genus

In the 21st century, Iguanodon material has been used in the search for dinosaur biomolecules. In research by Graham Embery et al., Iguanodon bones were processed to look for remnant proteins. In this research, identifiable remains of typical bone proteins, such as phosphoproteins and proteoglycans, were found in a rib. In 2007, Gregory S. Paul split I. atherfieldensis into a new, separate genus, Mantellisaurus which has been generally accepted. In 2009 fragmentary iguanodontid material was described from upper Barremian Paris Basin deposits in Auxerre, Burgundy. While not definitively diagnosable to the genus/species level, the specimen shares "obvious morphological and dimensional affinities" with I. bernissartensis.

In 2010, David Norman split the Valanginian species I. dawsoni and I. fittoni into Barilium and Hypselospinus respectively. After Norman 2010, over half a dozen new genera were named off English " Iguanodon" material. Carpenter and Ishida in 2010 named Proplanicoxa, Torilion and Sellacoxa while Gregory S. Paul in 2012 named Darwinsaurus, Huxleysaurus and Mantellodon and Macdonald et al. in 2012 named Kukufeldia. These species named after Norman 2010 are not considered valid and are considered various junior synonyms of Mantellisaurus, Barilium and Hypselospinus.

In 2011, a new genus Delapparentia was named for a specimen in Spain that was originally thought to belong to I. bernissartensis. The previous identification was subsequently reaffirmed in a new analysis of individual variation in the Belgian specimens, finding that the Delapparentia specimen was within the range of I. bernissartensis. In 2015 a new species of Iguanodon, I. galvensis, was named based on material including 13 juvenile (perinate) individuals found in the Camarillas Formation near Galve, Spain. In 2017 a new study was done of I. galvensis, with further evidence of distinctiveness from I. bernissartensis including several new autapomorphies. It was also found that the Delapparentia holotype (which is also from the Camarillas Formation) was not distinguishable from either I. bernissartensis or I. galvensis.