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| Brighstoneus simmondsi Lockwood, Martill & Maidment, 2021 Life restoration by John Sibbick. |
Abstract
A new genus and species of non-hadrosaurid hadrosauriform dinosaur, Brighstoneus simmondsi gen. et sp. nov., is described from the Lower Cretaceous Wessex Formation of the Isle of Wight. The new taxon has two autapomorphies, a nasal having a modest nasal bulla with convex sides, and primary and accessory ridges on the lingual aspect of the maxillary crown. The dentary has at least 28 alveolar positions, which is the highest number recorded in an ornithopod with non-parallel sided alveoli, creating a character combination that is unique within Iguanodontia. The hadrosauriform fauna of the Barremian–Aptian Wealden Group on both the Isle of Wight and mainland England has been represented for almost a century by just two taxa, the robust Iguanodon bernissartensis and the more gracile Mantellisaurus atherfieldensis, with referred material often being fragmentary or based on unassociated elements. This discovery increases the known hadrosauriform diversity in England and, together with recent discoveries in Spain, suggests that their diversity in the upper Wealden of Europe was considerably wider than initially realized. This find also has important implications for the validity of the Mantellisaurus atherfieldensis hypodigm, and a reassessment of existing material is suggested.
Keywords: Iguanodontia, Hadrosauriformes, diversity, Wealden Group, Lower Cretaceous, Isle of Wight
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| Figure 10. Preliminary reconstructions of the skulls of A, Brighstoneus simmondsi gen. et sp. nov. (MIWG 6344) and B, Mantellisaurus atherfieldensis (NHMUK PV R5764) in lateral view. Shaded areas represent material present in the holotypes. Scale bar = 100 mm. |
Systematic palaeontology
Dinosauria Owen, 1842
Ornithischia Seeley, 1887
Ornithopoda Marsh, 1881
Iguanodontia Dollo, 1888
Ankylopollexia Sereno, 1986
Styracosterna Sereno, 1986
Hadrosauriformes Sereno, 1997
Brighstoneus gen. nov.
Etymology: Brighstoneus is named after the village of Brighstone on the Isle of Wight, which is close to the excavation site and was home to the Reverend William Fox, a celebrated Victorian fossil collector whose discoveries had a major impact on early dinosaurian research.
Locality and horizon: Wessex Formation, early Barremian, Lower Cretaceous. MIWG 6344 was excavated during 1978, from a plant debris bed (L9 of Stewart 1978) to the west of Grange Chine on the south coast of the Isle of Wight (Fig. 2).
Brighstoneus simmondsi gen. et sp. nov.
Etymology: The specific name honours Mr Keith Simmonds who made the discovery of the specimen.
Holotype: MIWG 6344, a partial skeleton composed of the following elements: dorsal process of right premaxilla; both maxillae; both jugals; left palpebral; left nasal; both dentaries; predentary; one transitional dorsal and seven dorsal vertebrae; sacrum; six caudal vertebrae; dorsal ribs, nine from the left side and five from the right side; both ilia; right ischium; possible prepubic process; and the right femur. Some parts of the same individual (including two dorsal vertebrae and other fragments) remain in private ownership and are not described herein.
Diagnosis:
Differs from all other iguanodontians by possessing the following autapomorphies and unique combination of characters (autapomorphies indicated with an asterisk): maxillary crowns possessing both a primary ridge and mesially placed accessory ridges on the lingual surface*; nasal expanded postnarially to produce a modest nasal bulla with convex lateral walls*. A character combination of at least 28 dentary tooth positions in a dentary with one active crown and one replacement tooth for each position and non-parallel alveolar septa.
In addition, Brighstoneus can be distinguished from other Barremian–Aptian Wealden Group iguanodontians by possession of the following combination of features: ratio of precoronoid length of the dentary to minimum depth > 6.0; coronoid process projects at approximately 90° with respect to the dorsal margin of dentary; bilobed ‘heart-shaped’ ventral predentary process with prominent anterior denticles with concave mesial and distal edges; posteriorly positioned maxillary ascending process in lateral view with length of the anterior section approximately twice the length of the posterior section; prominent anterodorsal process present on maxilla; anterior (maxillary) process of jugal relatively long (60% of overall length) and tapers distally to form a triangular ending; ventral section of the posterior margin of the jugal (heel) projects posteriorly to form a spur-like feature; in dorsal view the jugal is straight; ventral border overlapped by maxillary process of premaxilla; anteroventral nasal process forms posteroventral margin of external narial opening; ventral surface of ischiadic peduncle of ilium parallel with the anteroventral margin of the postacetabular process; ischiadic peduncle of ilium has flat lateral wall with no pronounced posterolateral boss; ventral shelf at base of iliac preacetabular process weakly developed; dorsoventrally deep preacetabular process with little or no axial twist; deep and short iliac central plate with ratio of depth to length > 1.2.
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| Brighstoneus simmondsi gen. et sp. nov. Life restoration by John Sibbick. |
Conclusions:
Brighstoneus simmondsi is recognized as a new genus and species of hadrosauriform ornithopod from the Wealden Group of the Isle of Wight, on the basis of two autapomorphies and a unique combination of characters. It is likely that the holotype specimen is ∼4 Ma older than that of Mantellisaurus atherfieldensis, reinforcing the view that the Wealden Group is likely to have supported a higher diversity of iguanodontians than previously realized, both in the Wessex Formation and perhaps in coeval mainland exposures. This study also has systematic implications, questioning the validity of the composite operational taxonomic unit that has generally been used to score Mantellisaurus atherfieldensis in phylogenetic analyses. To provide better resolution of relationships within Iguanodontia and a more complete understanding of iguanodontian alpha diversity in the Wessex Sub-basin, a reassessment of Isle of Wight material is necessary.
Jeremy A. F. Lockwood, David M. Martill and Susannah C. R. Maidment. 2021. A New Hadrosauriform Dinosaur from the Wessex Formation, Wealden Group (Early Cretaceous), of the Isle of Wight, southern England. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2021.1978005