Fig 1.- Hypsilophodon foxii.
An Early Cretaceous lithostratigraphic unit called the “Wealden Group” in Southern England is famous for the many remains of dinosaurs and other prehistoric critters that were found in there. The name is derived from an originally heavily forested area in Sussex, Surrey and Kent known as “the Weald” (forest in Anglo-Saxon) and is subdivided into the “Lower Wealden Group” (Berriasian-Valanginian) and the “Upper Wealden Group” (Hauterivian-Lower Aptian). We’ve already talked about the Ornithopods of the Lower Wealden in two of its formations, the Wadhurst Clay and Turnbridge Wells Sand Formations (See Ornithopods of the British Isles, Part I). Let’s now review the comparatively richer Upper Wealden Group Ornithopod fauna from the Wessex and Vectis formations (Barremian to Lower Aptian) that contains as of 2011, 6 species.
Fig 2.- Highly speculative reconstruction of Valdosaurus canaliculatus as a dryosaur.
Hypsilophodon foxii is known from several well-preserved skeletons from the Isle of Wight. This lightly built bipedal ornithopod measuring about 2 meters in length was once thought to be a juvenile Iguanodon. For a century, it was also thought to be arboreal until Peter Galton disproved this hypothetical lifestyle with solid anatomical evidences in 1974.
Fig 3.- Dollodon seelyi, a 6.5 m long gracile iguanodont.
Next in size comes the obscur Valdosaurus canaliculatus (Originally "Dryosaurus canaliculatus"), also from the Isle of Wight, based on a pair of femora of possibly juvenile specimens. The current best guess is that it was a medium-size Dryosaur. The dubious “Camptosaurus” valdensis might be the same animal.
Iguanodonts are represented by the 6.5-meter long facultative bipedal form Dollodon seelyi (Originally “Iguanodon seelyi”) and the massively built 8-meter long quadrupedal Iguanodon bernissartensis, the only one of the several beasts that was named Iguanodon to retain the name without quotes (For the anecdote, the ICZN has, in year 2000, made I. bernissartensis the new type species of Iguanodon, because the former type, “I. anglicus” was found to be dubious). These two species are known from several remains found both in Southern England and the contemporary Sainte-Barbe Clays Formation in Belgium. Carpenter and Ishida have named a third species, Proplanicoxa galtoni, based on a set of postcranial elements in 2010.
Fig 4.- The heavily built 8 m long quadrupedal Iguanodon bernissartensis.
In the slightly younger Vectis Formation of the Upper Wealden Group (Early Aptian), Iguanodon bernissartensis is associated with a fourth iguanodont, the gracile and probably bipedal form Mantellisaurus atherfieldensis (Originally “Iguanodon atherfieldensis”). Andrew McDonald (2011) has recently questioned the validity of the genera Dollodon and Proplanicoxa claiming their strong similarities with Mantellisaurus. However, the author has since withdrawn the paper accepted for publication in Cretaceous Research. The fragmentary fossils named Sphenospondylus gracilis and Vectisaurus valdensis are considered to be synonyms of Mantellisaurus.
Fig 5.- The gracile iguanodont 6 m long and probably bipedal Mantellisaurus atherfieldensis.
All is not settled yet in the wild world of the British Ornithopods. For instance, one specimen of “Iguanodon mantelli” from Maidstone, Kent which was referred to Mantellisaurus by Greg Paul, is seen as a different species awaiting a new generic name by Carpenter and Ishida. The Maidstone specimen is apparently the youngest of all Iguanodonts of the British Isles dating from the Late Aptian stage of the Lower Cretaceous.
Concerning the Hadrosaurs (the so-called “Duck-billed dinosaurs”), the most derived and diversified group of Ornithopods, they were certainly present in the British Isles during the Late Cretaceous period but so far the fossil record has been elusive consisting of isolated dubious teeth (which might as well belong to late Iguanodonts), such as the one named “Iguanodon hillii” from the Cenomanian Lower Chalk Formation of Hertfordshire and “Trachodon cantabrigiensis” from the Cambridge Green Sand Formation of Cambridgeshire (Albian-Cenomanian).
This concludes our quick tour of the Ornithopods of the United Kingdom.
Carpenter, K. and Ishida, Y. 2010. Early and "Middle" Cretaceous Iguanodonts in Time and Space. Journal of Iberian Geology 36 (2): 145–164.
Galton, P.M. 1975. English hypsilophodontid dinosaurs (Reptilia: Ornithischia). Palaeontology 18(4):741-752.
Galton, P. M. 1977. The Upper Jurassic dinosaur Dryosaurus and a Laurasia-Gondwana connection in the Upper Jurassic. Nature 268(5617):230-232.
McDonald, A. T. 2011. The status of Dollodon and other basal iguanodonts (Dinosauria: Ornithischia) from the upper Wealden beds (Lower Cretaceous) of Europe. Cretaceous Research advance online publication.
Naish, D. and Martill, D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164:493-510.
Paul, G.S. 2007. Turning the old into the new: a separate genus for the gracile iguanodont from the Wealden of England. In K. Carpenter (ed.), Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press, Bloomington 69-77.
Paul, G. S. 2008. A revised taxonomy of the iguanodont dinosaur genera and species. Cretaceous Research 29(2):192-216.