This contribution concerns itself with updating our current understanding of the anatomy, taxonomy and systematics of an Early Cretaceous group of neoiguanodontians from the Wealden of northwest Europe (Fig. 2.1). Given their older chronostratigraphic occurence relative to hadrosaurids, these taxa contribute to an analysis of taxa that are considered topologically basal to hadrosaurids. This review probes our understanding of an important phase in ornithopod evolution, and highlights areas where more research is needed.
Institutional abbreviations MIWG, Museum of the Isle of Wight Geology, Sandown, Isle of Wight, U.K.; NHMUK, Natural History Museum, London, U.K.; RBINS [formerly IRSNB], Royal Belgian Institute of Natural Sciences, Brussels, Belgium.
A REVIEW OF WEALDEN IGUANODONTIANS
A large number of names have become associated with medium-to-large-bodied Wealden-aged Iguanodon-like ornithopods, or iguanodonts (Fig. 2.2); these include historical names such as Vectisaurus valdensis Hulke, 1879 (Norman, 1990); Sphenospondylus gracilis Lydekker, 1888; and Iguanodon seelyi Hulke, 1882. However, renewed scientific interest in the Wealden since 2008 has resulted in a proliferation of additional taxa that have been recognized on the morphological variation present in the sample. Recently proposed taxa include Dollodon bampingi (Paul, 2008); Barilium dawsoni (Norman, 2010); Hypselospinus fittoni (Norman, 2010); Kukufeldia tilgatensis (McDonald, Barrett, and Chapman, 2010); Torilion dawsoni (Carpenter and Ishida, 2010); Wadhurstia fittoni (Carpenter and Ishida, 2010); Sellacoxa pauli (Carpenter and Ishida, 2010); Proplanicoxa galtoni (Carpenter and Ishida, 2010); Dollodon seelyi (Carpenter and Ishida, 2010); Huxleysaurus hollingtoniensis (Paul, 2012); Darwinsaurus evolutionis (Paul, 2012); and Mantellodon carpenteri (Paul, 2012).
| WEALDEN TAXA (Norman/McDonald) | WEALDEN TAXA (paul, Carpenter & Ishida, Hulke, Lydekker) |
| Barremian/Aptian | Barremian/Aptian |
| Iguanodon bernissartensis Boulenger, 1881 [v] | l. bernissartensis [v] |
| l. seelyi Hulke, 1882 [jss] | |
| Dollodon seelyi (Carpenter & Ishida, 2010) [nd-jss] | |
| Mantellisaurus atherfieldensis (Hooley, 1925) [v] | M. atherfieldensis [v] |
| Vectisaurus valdensis Hulke, 1879 [nd] | |
| Sphenospondylus gracilis (Lydekker, 1888) [nd] | |
| Proplanicoxa galtoni Carpenter & Ishida, 2010 [nd-jss] | |
| Dollodon bampingi Pau, 2008 [nd-jss] | |
| *Mantellodon carpenteri Paul, 2012 [nd-jss] | |
| Valanginian | Valanginian |
| Barilium dawsoni (Lydekker, 1888) [v] | B.dawsoni [v] |
| Iguanodon anglicus Holl, 1829 [servo statua] | Kukufeldia tilgatensis McDonald, Barrett & Chapman, 2010 [nd-jss] |
| Torilion dawsoni Carpenter & Ishida, 2010 [jos] | |
| Sellacoxa pauli Carpenter & Ishida, 2010 [nd-jss] | |
| Hypselospinus fittoni (Lydekker, 1889) [v] | H. fittoni [v] |
| Wadhurstia fittoni Carpenter & Ishida, 2010 [jos] | |
| Huxleysaurus hollingtoniensis Paul, 2012 [nd-jss] | |
| Darwinsaurus evolutions Paul, 2012 [nd-jss] |
2.2. The taxonomy of Wealden iguanodontian dinosaurs tabulated according to (in the left column) the interpretation of Norman (2010, 2011a, 2011b, 2012, 2013, in press; McDonald, pers. comm., 2012), compared with the taxonomy (in the right column) introduced by Paul (2008); Carpenter and Ishida (2010); and McDonald, Barrett, and Chapman (2010). Asterisk indicates non-Wealden taxon. Abbreviations: nd, nomen dubium; jos, junior objective synonym; jss, junior subjective synonym; v, valid taxon.
This proliferation of Wealden taxa suggests that there was considerable taxonomic diversity among these animals during Wealden time (Fig. 2.2). Recognition of this diversity is significant, because phylogenetic analyses suggest these taxa provide insights into the morphological changes that occurred in the evolutionary transition to early hadrosauroids from more primitive iguanodonts. However, the validity of a number of these recently named taxa has been questioned (Norman, 2013). The taxa erected by Paul, and Carpenter and Ishida are poorly – or incorrectly – diagnosed. Based on detailed study of the original material, many of these new taxa have been considered nomina dubia that are either unambiguously or subjectively synonymous with one of just four osteologically distinct Wealden-aged iguanodont taxa: Barilium, Hypselospinus, Iguanodon, and Mantellisaurus (Norman, 2011a, 2011b, 2012, 2013, in press; McDonald, 2012a). In addition, it appears that these novel, but dubious, taxa were proposed (and, in part, justified) on the basis of a fundamental lack of understanding of the stratigraphy of the Wealden and the provenance of the taxa that have been collected from Wealden exposures (Norman, 2013). The anatomy and spatio-temporal distribution of the iguanodonts from the Weald is reviewed below.
SYSTEMATIC PALEONTOLOGY
ORNITHISCHIA Seeley, 1887
ORNITHOPODA Marsh, 1881
DRYOMORPHA Sereno, 1986
ANKYLOPOLLEXIA Sereno, 1986
BARILIUM Norman, 2010 BARILIUM DAWSONI (Lydekker, 1888)
Lydekker (1888) described the partial skeleton of a large iguanodont that had been recovered during quarrying through ferruginous sandstones at Shornden, an open-cast quarry on an area of land about 1.5 km north of Hastings town center (Norman, 2011a). The material included dorsal and caudal vertebrae, portions of the pelvis, and parts of the hindlimb. The ilium was regarded as sufficiently distinct from anything previously described as pertaining to Iguanodon that it merited the establishment of a new taxonomic name, I. dawsoni. Norman (2010, 2011a) redescribed the type material, presented a formal diagnosis, and proposed the new combination Barilium dawsoni (Lydekker, 1888).
Taxonomic Discussion
McDonald et al. (2010) proposed that an isolated,