November 15, 2010 | 2
One of the most familiar and historically significant of dinosaur names is Iguanodon, named in 1825 for teeth and bones discovered in the Lower Cretaceous rocks of the Cuckfield region of East Sussex, southern England. Everyone who’s ever picked up a dinosaur book will be familiar with the legendary – yet mostly apocryphal – tale where Gideon Mantell and his wife Mary obtained and interpreted these first scrappy fossils.
Mantell and his colleagues were of course unaware of the fact that Iguanodon was but one among tens or hundreds of similar ornithopod dinosaurs. Quite naturally, the name Iguanodon was gradually applied to the fossils of numerous different Lower Cretaceous ornithopod species. By the late 20th century, the name Iguanodon was being used for ornithopods from across Europe, Asia, northern Africa and North America. Some of these were similar in age to Mantell’s Cuckfield fossils, but others were older, or younger… sometimes much younger. Furthermore, by the 1990s it had become clear that these animals were not as similar as experts had initially assumed: Iguanodon not only included species that were spread across about 40 million years of geological history, it also housed substantially disparate animals. Among the better known species, for example, there was relatively small, gracile, short-snouted, short-armed I. atherfieldensis (named from the Isle of Wight, England, in 1925) and enormous, heavily built, long-snouted, long-armed I. bernissartensis (named from Bernissart, Belgium, in 1881). Both species were comprehensively monographed by David Norman during the 1980s (Norman 1980, 1986) [the composite image above includes colour restorations by Steveoc 86 (from Wikipedia) and skull reconstructions by Greg Paul ©, used with permission)].
Murmurings in the literature implied that people were, increasingly, thinking that Iguanodon of tradition (Iguanodon sensu lato from hereon) really was artificial; an artefact of history. Things finally began moving in the late 1990s. During the 1980s a particularly distinctive ornithopod with an enormous nose was discovered in Mongolia. Initially referred to the species Iguanodon orientalis (named in 1952 for a maxilla, scapula and other fragments), it was clearly highly distinct compared to Iguanodon sensu lato and not obviously closely related to it. Accordingly, in 1998, Norman gave it the new name Altirhinus kurzanovi (Norman 1998) [Altirhinus skull shown here, by Ghedoghedo, from Wikipedia].
Rescuing Iguanodon, and recognising Owenodon
So far so good, but many other problems remained. Mantell’s original Iguanodon material was given the name I. anglicus in 1829* but this material has generally been regarded as non-diagnostic. This is a problem: if the type species for Iguanodon is a nomen dubium (a name based on insufficient type material that is not definitely synonymous with any other named species), the generic name Iguanodon is too.
* Actually, the name was first spelt I. anglicum. It was corrected to I. anglicus by Norman (1986).
In order to save the name Iguanodon, Charig & Chapman (1998) proposed that the Belgian species Iguanodon bernissartensis be made the new type species for the genus. As Dick Moody and I recently argued (Moody & Naish 2010), this proposal is sensible given that I. bernissartensis is anatomically well known, well described in the literature, and associated – without exception – with the name Iguanodon. On the other hand, however, the proposal is slightly problematic given that I. bernissartensis is likely a very different animal from the one represented by the I. anglicus remains. Anyway, the ICZN later ruled in favour of Charig & Chapman’s (1998) proposal, so the name Iguanodon is forever tied to the species I. bernissartensis.
A second species became removed from Iguanodon in 2002 when Norman & Barrett (2002) argued that Iguanodon hoggii – named in 1874 for a distinctive lower jaw [shown here, from its original, 1874 description] from the Berriasian part of the Purbeck Limestone Group of Durlston Bay, Dorset – was actually a species of Camptosaurus. Peter Galton later argued that the Purbeck iguanodontian is neither a species of Iguanodon nor of Camptosaurus, and that its unique features make it deserving of its own genus. The name Owenodon hoggii was born (Galton 2009). I think that Norman had planned to use the new name Durlstonia for this species, but it looks like Galton beat him into publication.
Even with Altirhinus and Owenodon out of the equation, Iguanodon sensu lato remained sprawling and home to many uneasy bedfellows. In a review of British ornithischians published in 2008, David Martill and I remained convinced that “Iguanodon is the ornithopod version of Cetiosaurus and Megalosaurus: a taxonomic dumping ground for any ornithopod remains that are not clearly referable to any other named British taxon. The status and phylogenetic relationships of many of the referred species and specimens requires further study” (Naish & Martill 2008, p. 620).
Mantellisaurus and Dollodon
While our article was in review, Greg Paul published a brief paper in which he argued that the Isle of Wight species I. atherfieldensis was also morphologically ‘distinct enough’ from I. bernissartensis to deserve its own generic name (note also that I. atherfieldensis and I. bernissartensis do not always group together in cladistic analyses). Paul (2006) chose the name Mantellisaurus, which is kind of inappropriate given that Mantell had nothing to do with the discovery or naming of atherfieldensis (the namer was actually Reginald Walter Hooley, a businessman who discovered and described Isle of Wight fossils in his spare time. His description of Mantellisaurus was published posthumously; he died in 1923). Mantellisaurus has often been regarded as very similar to I. bernissartensis (some authors have even gone as far as suggesting that the two might be sexual dimorphs of the same species), but they’re really very different [Hooley’s skull reconstruction of Mantellisaurus is shown here]. Here, things became somewhat complicated…
Paul’s conclusions about the distinction of Mantellisaurus relative to I. bernissartensis initially rested on his reconstruction of a Mantellisaurus specimen (known technically as IRSNB 1551) found at Bernissart, alongside the many I. bernissartensis specimens (Norman 1986). This is the specimen that Norman (1986) described in his classic monograph on Mantellisaurus atherfieldensis.
But IRSNB 1551 isn’t the type specimen for this species: that honour goes to Hooley’s Isle of Wight specimen (known technically as NHMUK R5764). Noting that the latter seemed rather different in some respects from the 1551 specimen, Paul (2008) produced a new skeletal reconstruction. To his surprise, it seemed to be a substantially different animal from IRSNB 1551. While the 1551 specimen impressed Paul in being proportionally long-jawed, in possessing an unusually high lower jaw tooth count, and in having proportionally long forelimbs (about 55 percent of hindlimb length) and tall neural spines, Hooley’s Isle of Wight animal had a shorter, deeper skull, proportionally short forelimbs (about 50% of hindlimb length) and a proportionally larger, deeper pelvis. IRSNB 1551 seemed perfectly capable of quadrupedal locomotion, while the Mantellisaurus holotype looked more like a habitual biped. The outcome from all of this – according to Paul (2008) – is that IRSNB 1551 is not a Belgian representative of Mantellisaurus at all, but in fact represents a new iguanodontian species. Paul named it Dollodon bampingi [Paul’s skeletal reconstructions of Dollodon and Mantellisaurus are shown here, with Dollodon at top. Images © Greg Paul, used with permission]. As we’ll see later, this proposal has proved controversial.
As of 2008 then, ‘Iguanodon’ of tradition had been argued to be a composite of Iguanodon bernissartensis, Altirhinus, Owenodon, Mantellisaurus and Dollodon. But there’s more… much more, as we’ll see in part 2.
Charig, A. J. & Chapman, S. D. 1998. Iguanodon Mantell, 1825 (Reptilia, Ornithischia): proposed designation of Iguanodon bernissartensis Boulenger in Beneden, 1881 as the type species, and proposed designation of a lectotype. Bulletin of Zoological Nomenclature 55, 99-104.
Galton, P. M. 2009. Notes on Neocomian (Lower Cretaceous) ornithopod dinosaurs from England – Hypsilophodon, Valdosaurus, “Camptosaurus”, “Iguanodon” – and referred specimens from Romania and elsewhere. Revue de Paleobiologie 28, 211-272.
Moody, R. T. J. & Naish, D. 2010. Alan Jack Charig (1927-1997): an overview of his academic accomplishments and role in the world of fossil reptile research. In Moody, R. T. J., Buffetaut, E., Naish, D. &Martill, D. M. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications 343, 89-109.
Naish, D. & Martill, D. M. 2008. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, London 165, 613-623.
Norman, D. B. 1980. On the ornithischian dinosaur Iguanodon bernissartensis of Bernissart (Belgium). Mémoires de l’Institut Royal des Sciences Naturelles de Belgique 178, 1-105.
- . 1986. On the anatomy of Iguanodon atherfieldensis (Ornithischia: Ornithopoda). Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 56, 281-372.
- . 1998. On Asian ornithopods (Dinosauria: Ornithischia). 3. A new species of iguanodontid dinosaur. Zoological Journal of the Linnean Society 122, 291-348.
Paul, G. S. 2006 (dated 2007). Turning the old into the new: a separate genus for the gracile iguanodont from the Wealden of England. In Carpenter, K. (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press (Bloomington & Indianapolis), pp. 69-77.
- . 2008. A revised taxonomy of the iguanodont dinosaur genera and species. Cretaceous Research 29, 192-216.
About The Author: Darren Naish is a British palaeozoologist and writer who mostly works on Cretaceous dinosaurs and pterosaurs. He blogs about animals – living and extinct – at Tetrapod Zoology, and has just published a compilation of Tet Zoo blog articles in book form (tetrapods are four-limbed vertebrates: amphibians, reptiles, birds and mammals). Other recent books include The Great Dinosaur Discoveries and Dinosaurs Life Size. He is based at the University of Portsmouth, U.K.
The views expressed are those of the author and are not necessarily those of Scientific American.