Evidence for Diversity and Variation in the Early Cretaceous Iguanodontian Dinosaurs of the Isle of Wight, Southern England

Abstract

The Wealden Group in southern England is represented by non-marine strata from the end of the Berriasian to the early Aptian (Early Cretaceous) and is historically important, being the source of the fossils that inspired Gideon Mantell to name Iguanodon, and which allowed Richard Owen to invent the Dinosauria in 1841. It also represents an important stage in the evolution of Iguanodontia, as they moved from low levels of diversity in the Late Jurassic to a burgeoning of genera in the Aptian and Albian. The Isle of Wight exposures are rich in iguanodontian fossils from the latest Hauterivian to the early Aptian and produced one of England’s most complete dinosaur skeletons (Mantellisaurus atherfieldensis) in 1914. Since that time all medium-large iguanodontian material from the Barremian and early Aptian of the Wealden Group has been either referred to this taxon or synonymised with it. This study focuses on iguanodontian material from the Isle of Wight and uses data on metrics and morphology from the extensive collections held principally at the Natural History Museum and Dinosaur Isle Museum on the Isle of Wight, to assess variation and diversity. Due to concerns over the validity of the Mantellisaurus atherfieldensis hypodigm, the original specimen was examined and topographically scanned, and a revised osteology produced, based solely on the holotype, with autapomorphies and unique character suites identified. Comparison with other Isle of Wight material showed considerable variation, which in some more complete specimens was best explained in terms of interspecific variation. This required the erection of three new taxa of moderately large iguanodontians (Brighstoneus simmondsi, Comptonatus chasei and Istiorachis macarthurae) that had previously been assigned formally or informally to Mantellisaurus atherfieldensis. This study has opened the door to a greater understanding of iguanodontian anatomy and diversity in the Wealden Group exposures on the Isle of Wight, and also generated a large number of taxonomic differences. These require additional work to isolate the character states that will hopefully allow a fuller elucidation of the currently, poorly resolved phylogeny of the group.

Date of Award	12 Jun 2024
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	David Martill (Supervisor), David Kendrick Loydell (Supervisor) & Susie Maidment (Supervisor)