Mantellisaurus skull

The search for the real Iguanodon

3 July 2017

Iguanodon was one of the first three dinosaurs to be discovered, but the renowned reptile may have swept up several misidentified skeletons along in its wake. 

One of the world's most complete skeletons of Mantellisaurus atherfieldensis is on display in the Museum's recently redeveloped Hintze Hall.

However, the dinosaur has only recently claimed its true identity, after spending over 80 years known to the world as a species of Iguanodon.

Dinosaur 'dumping ground'

In 1825, Dr Gideon Algernon Mantell - an English surgeon, geologist and palaeontologist - described several prehistoric teeth from the Wealden district of East Sussex.

They looked like those of an iguana but considerably larger, so Mantell named his newfound discovery Iguanodon.

Mantell's collection of fossilised teeth served as the foundation for defining the genus Iguanodon. Since the original discovery, we now understand Iguanodon to be larger and more complex than most of the other dinosaur genera described since. 

Illustration of Iguanodon mantelli in a kangeroo-like stance

Early reconstructions of Iguanodon showed the dinosaur standing in a kangaroo-like stance © H.N. Hutchinson/ Wikimedia Commons

 

The range of dinosaurs that were assigned to Iguanodon spanned 40 million years of geological history in Europe, Africa, North America and Asia.

In 2008, palaeontologists Darren Naish and David Martill described the genus, along with the British dinosaur genera Cetiosaurus and Megalosaurus, as 'taxonomic dumping grounds' for species that did not fit seamlessly into any other group.

Recent studies based on more complete Iguanodon remains and the reassessment of old specimens in Museum collections have led to refining the genus, with some former Iguanodon species now reassigned to separate, newly described genera.  

But there has always been some debate over which dinosaur species belong to particular genera, and some of these changes are likely to remain subject to discussion for years to come. 

Mistaken identity

Amateur palaeontologist Reginald Walter Hooley discovered a new species of what he believed to be Iguanodon in 1914.

In 1925 he settled on the species name Iguanodon atherfieldensis, after the small village of Atherfield near the discovery site on the Isle of Wight.

But the bones he found turned out to be a different dinosaur altogether.

The dinosaur was renamed Mantellisaurus atherfieldensis in 2007, as part of a revision of the Iguanodon genus. 

Iguanodon and its close relatives were previously believed to walk on two legs in a kangaroo-like posture. More recent studies suggest that they were more likely to have walked on all four legs.

Illustration of Mantellisaurus

Mantellisaurus is now thought to be semi-quadrupedal, and probably had a more crouched posture ©Steveoc 86/ Wikimedia Commons

 

But Mantellisaurus has notably shorter forelimbs - meaning perhaps the dinosaur was only semi-quadrupedal - and only used all four legs at slow speeds or when standing still. 

Additionally, Mantellisaurus, which would have lived during the Early Cretaceous Period around 125-110 million years ago in what is now western Europe, was of a lighter build than its previously associated Iguanodon relations such as I. bernissartensis.  

Despite their differences, Mantellisaurus and Iguanodon do retain some similarities.

Both are members of the same group of dinosaurs called Iguanodontia and possessed large thumb spikes, which are thought to have been used as the dinosaur's primary defence against predators.

A world-class specimen

Before its relocation to Hintze Hall, the Mantellisaurus skeleton, which is made up of 80% to 90% real bone, was suspended in the Museum's Dinosaurs gallery.

Its move has given conservators an opportunity to carry out a deep clean, as well as check for any necessary restorative works and review historical repairs. 

The Museum's Mantellisaurus skeleton in Hintze Hall

The Mantellisaurus skeleton was cleaned and checked for any necessary repairs before being settled into its new home in Hintze Hall

 

Fossil preparator Mark Graham, who worked on the specimen, says, 'Although some fractures have occurred after many years on display, the specimen, which is the original described by Hooley in 1925, is in very good condition.'

The conservation team had to carry out some careful repairs. For the purposes of clarity and future study of this scientifically significant specimen, it is clear where fixes have been carried out.

'Conservation ethics have moved on,' says Mark. 'So although we want the specimen to look complete, we don't want to mislead people on what is real and what is not.

'But where repairs were necessary, we've used methods and materials that are reversible - so if we ever want to undo the work, we can without damaging the specimen.'

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