The status of Dollodon and other basal iguanodonts (Dinosauria: Ornithischia) from the Lower Cretaceous of Europe
Introduction
Europe boasts one of the richest records of Early Cretaceous basal iguanodonts in the world, and yet 186 years after Mantell’s (1825) initial description of Iguanodon, the taxonomy of Europe’s basal iguanodonts is still in need of resolution. Following the designation of Iguanodon bernissartensis as the type species of the genus (Charig and Chapman, 1998), several authors have recently reassigned various species and specimens long called Iguanodon to new genera (Carpenter and Ishida, 2010, Galton, 2009, McDonald et al., 2010, Norman, 2010, Paul, 2006, Paul, 2008).
One such species is Iguanodon atherfieldensis, named by Hooley (1925) based upon a nearly complete skull and postcranium (NHMUK R5764) from the Vectis Formation of the Isle of Wight (Naish and Martill, 2008, Norman, 1986). Norman (1986) referred a singular gracile skeleton (IRSNB 1551) from the Bernissart Quarry in Belgium to I. atherfieldensis. Paul (2006) judged I. atherfieldensis to be sufficiently disparate from I. bernissartensis to warrant its removal to the new genus Mantellisaurus. Finally, Paul (2008) removed IRSNB 1551 from Mantellisaurus atherfieldensis and made it the type specimen of the novel genus and species Dollodon bampingi.
Unfortunately, Paul’s (2008) diagnoses of M. atherfieldensis and D. bampingi are inadequate to distinguish the two taxa from each other and from other basal iguanodonts, consisting mostly of subjective qualitative statements of quantitative characteristics (e.g., “posterior portion of jugal short”, Paul, 2008: 200). In an effort to evaluate the validity of D. bampingi and enhance the diagnosis of M. atherfieldensis, I examined firsthand NHMUK R5764, IRSNB 1551, and other basal iguanodont specimens in the NHMUK, IRSNB, and MIWG collections.
Carpenter and Ishida (2010) contended that the ilia of IRSNB 1551, the holotype of D. bampingi, are indistinguishable from NHMUK R2502, the ilium of the syntype of Iguanodon seelyi (Hulke, 1882); they therefore made I. seelyi the type species of Dollodon, rendering D. bampingi a junior synonym. However, this taxonomic decision is unjustified because NHMUK R2502 bears a much closer resemblance to the ilia of IRSNB 1534, the lectotype of I. bernissartensis; the two specimens are alike in their gently convex dorsal margins and tapering postacetabular processes that lack a break in slope along their dorsal margins (Fig. 1). These morphologies differ from the ilia of IRSNB 1551, as well as those of NHMUK R5764 (holotype of Mantellisaurus atherfieldensis), MIWG 6344, and NHMUK R11521, all of which have a straight dorsal margin and a sharp break in slope along the dorsal margin of the postacetabular process (Fig. 2). The other elements preserved in the syntype partial skeleton of I. seelyi (NHMUK R2502-R2509) are also virtually indistinguishable from the corresponding elements of I. bernissartensis specimens from the Bernissart Quarry. Therefore, I. seelyi is best considered a junior synonym of I. bernissartensis, as originally proposed by Norman (1986). This means that the proper type species of Dollodon is D. bampingi, and it is treated as such in this paper.
Institutional acronyms: CEUM, College of Eastern Utah Prehistoric Museum, Price, UT, USA; IRSNB, Institut royal des Sciences naturelles de Belgique, Brussels, Belgium; MIWG, Museum of Isle of Wight Geology (Dinosaur Isle Museum), Sandown, UK; NHMUK, Natural History Museum (formerly BMNH, British Museum of Natural History), London, UK; USNM, National Museum of Natural History, Washington, DC, USA; YPM, Yale Peabody Museum of Natural History, New Haven, CT, USA.
Section snippets
Materials and methods
In addition to NHMUK R5764 (holotype of M. atherfieldensis) and IRSNB 1551 (holotype of D. bampingi), I examined two other nearly complete associated skulls and postcrania, both from the Wessex Formation of the Isle of Wight: NHMUK R11521 and MIWG 6344. NHMUK R11521 was referred to as Mantellisaurus sp. and MIWG 6344 as Dollodon sp. by Paul (2008). The postcranial material of NHMUK R5764 is suspended several meters above the floor of the NHMUK dinosaur hall, and was thus difficult to view and
Original diagnostic characters
The cranial and postcranial skeletons of NHMUK R5764, IRSNB 1551, NHMUK R11521, and MIWG 6344 are virtually indistinguishable from each other. Nevertheless, Paul (2008) proposed that NHMUK R5764 and IRSNB 1551 are sufficiently different to warrant placement in the distinct taxa M. atherfieldensis and D. bampingi, respectively. To assess this hypothesis, it is necessary to evaluate the characters by which the diagnoses of the two taxa differ. In the following list, “M” stands for Mantellisaurus
Systematic paleontology
Dinosauria Owen, 1842
Ornithischia Seeley, 1887
Ornithopoda Marsh, 1881
Iguanodontia Dollo, 1888
Ankylopollexia Sereno, 1986
Styracosterna Sereno, 1986
Hadrosauriformes Sereno, 1997 (sensu Sereno, 1998)
Mantellisaurus atherfieldensis (Hooley, 1925) Paul, 2006
1925 Iguanodon atherfieldensis Hooley, p. 3
1986 Iguanodon atherfieldensis Norman, p. 283
2006 Mantellisaurus atherfieldensis Paul, p. 74
2008 Dollodon bampingi Paul, p. 200
Holotype. NHMUK R5764, nearly complete skull and postcranium.
Referred
Discussion and conclusions
In addition to M. atherfieldensis, D. bampingi, and I. bernissartensis, three other basal iguanodonts have been recognized from Lower Cretaceous rocks on the Isle of Wight: Sphenospondylus gracilis (Lydekker, 1888, Seeley, 1883), Vectisaurus valdensis (Hulke, 1879), and Proplanicoxa galtoni (Carpenter and Ishida, 2010). Sphenospondylus is based upon a series of six incomplete dorsal vertebrae (NHMUK R142) that do not present any features that would allow them to be associated with any other
Acknowledgements
I am very grateful to my advisor, Peter Dodson, for his tireless encouragement and for reading a rough draft of this paper. I am also grateful to Steve Hutt for discussions of MIWG specimens and Paul Barrett for measurements and photographs of the dentary of NHMUK R11521, and to both of them for the opportunity to work on specimens under their care. I thank the following people for access to and assistance with specimens under their care: J. Bartlett and J. Bird (CEUM); A. Folie and H. du
References (29)
A revised taxonomy of the iguanodont dinosaur genera and species
Cretaceous Research
(2008)- et al.
An Early Cretaceous lacustrine record: organic matter and organic carbon isotopes at Bernissart (Mons Basin, Belgium)
Palaeogeography, Palaeoclimatology, Palaeoecology
(2009) - et al.
Early and “Middle” Cretaceous iguanodonts in time and space
Journal of Iberian Geology
(2010) - et al.
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
(1998) Iguanodontidae et Camptonotidae
Comptes rendus de l’Académie des Sciences
(1888)The dinosaur Vectisaurus valdensis (Ornithischia: Iguanodontidae) from the Lower Cretaceous of England
Journal of Paleontology
(1976)The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic
Nature
(1977)Notes on Neocomian (Lower Cretaceous) ornithopod dinosaurs from England – Hypsilophodon, Valdosaurus, “Camptosaurus”, “Iguanodon” – and referred specimens from Romania and elsewhere
Revue de Paléobiologie, Genève
(2009)- et al.
PAST: Paleontological statistics software package for education and data analysis
Palaeontologia Electronica
(2001) On the skeleton of Iguanodon atherfieldensis sp. nov., from the Wealden Shales of Atherfield (Isle of Wight)
Quarterly Journal of the Geological Society of London
(1925)
Vectisaurus valdensis, a new Wealden dinosaur
Quarterly Journal of the Geological Society
Description of some Iguanodon-remains indicating a new species, I. seelyi
Quarterly Journal of the Geological Society
Note on a new Wealden iguanodont and other dinosaurs
Quarterly Journal of the Geological Society
Notice on the Iguanodon, a newly discovered fossil reptile, from the sandstone of Tilgate Forest, in Sussex
Philosophical Transactions of the Royal Society of London
Cited by (26)
English Wealden fossils: an update
2018, Proceedings of the Geologists' AssociationIndividual variation in the postcranial skeleton of the Early Cretaceous Iguanodon bernissartensis (Dinosauria: Ornithopoda)
2017, Cretaceous ResearchCitation Excerpt :When such variable characters cannot be avoided in systematics and phylogenetics, we therefore advise (1) to use the most frequent morphotype in the sample (e.g., dorsoventrally expanded axial neural spine, curved preacetabular process in the ilium, and curved ischiatic shaft in the ischium) so that the less frequent morphotypes are treated as aberrant forms; (2) to define the character in other ways (e.g., both the triangular and trapezoid fourth trochanter can be recognized as a tab-shaped fourth trochanter, as defined by Wu and Godefroit [2012: char. 103]), or (3) to indicate the total range in variation for the taxon in question (e.g., I. bernissartensis should be codified as having both a ‘mediolaterally thickened dorsal margin compared to the dorsal margin above pubic peduncle’ and a ‘thickened and laterally bulging everted rim along the dorsal margin’ in McDonald's [2012a: char. 112] dataset).
Perinates of a new species of Iguanodon (Ornithischia: Ornithopoda) from the lower Barremian of Galve (Teruel, Spain)
2015, Cretaceous ResearchCitation Excerpt :I. galvensis is different to other European Barremian hadrosauriforms. Highlighted below are the most important osteological differences with respect to taxa such as I. bernissartensis (Norman, 1980), Mantellisaurus atherfieldensis (Hooley, 1925; Norman, 1986; McDonald, 2012a) and the contemporaneous taxon Delapparentia turolensis (Ruiz-Omeñaca, 2011). The latter has been considered nomen dubium (Norman, 2014b); however, Gasca et al. (2015) restudied the holotype, validating the taxon.
Dinosaur footprints from the lower cretaceous of the algarve basin (Portugal): New data on the ornithopod palaeoecology and palaeobiogeography of the Iberian Peninsula
2013, Cretaceous ResearchCitation Excerpt :These dinosaurs would have had posterior limbs with a hip height of about 1.8 to 2.4 m and moved at speeds ranging between 3.1 and 4.4 km/h, based on the equations of Alexander (1976). The study of the European Early Cretaceous basal iguanodonts is in continuous review and quite a few osteological remains assigned to Iguanodon have been reassigned to new genera (e.g., Norman, 2002, 2004, 2010; Norman and Barrett, 2002; Paul, 2006, 2008; Naish and Martill, 2008; Galton, 2009; Carpenter and Ishida, 2010; McDonald et al., 2010; McDonald, 2012). Ornithopod remains have been known in Portugal since the nineteenth century in the coastal cliffs of Boca do Chapim, to the north of Cabo Espichel, near Sesimbra (see Rodrigues et al., 2008 for a historical review of the vertebrate fauna of this site).