Abstract
The iguanodontian dinosaurs lived from the Middle Jurassic to the Late Cretaceous on every continent. Their namesake Iguanodon was the second dinosaur ever to be named and described. Diverse and widespread, they were a group of ornithopods that were generally large, mainly quadrupedal, herbivorous animals, many of which possessed a uniquely specialised hand with a characteristic thumb-spike for the first digit. First described from the Wealden Formation of the U.K. in the 19th century, their taxonomic and systematic history has been long and convoluted, mainly due to the sheer amount of time in which they have been known, and early efforts made at their classification when the field of dinosaur palaeontology was still in its infancy. Often over-looked for more headline-grabbing specimens, the iguanodontians were nevertheless an important part of Mesozoic ecosystems, and this thesis seeks to answer some key questions regarding their inter-relationships.This work takes a multi-faceted approach to assessing the systematics and taxonomy of these animals. First, the impact of the state of the fossil record on interpreting trends
in dinosaur diversification rates is looked into, finding that it is very difficult, if at all possible, to tell if a clade was either thriving or declining at a particular point in time using only the fossil record, which by its very nature is incomplete and flawed. Next, previous attempts at producing a phylogeny of the iguanodontians are examined, they often involve the removal of many taxa or characters, and result in poorly resolved consensus trees. I find that iguanodontian datasets are no worse in condition than those of other dinosaurs, and in fact often contain data of a higher quality, with more fossil material than many other key clades, suggesting issues with taxonomy. To begin the process of revising the taxonomy of the iguanodontians, a full monographical redescription and 3D scan of the key British holotype Mantellisaurus is carried out, confirming its status as a non-hadrosaurid hadrosauroid. Further detailed taxonomic revisions then take place redefining the autapomorphies of many British Valanginian specimens, naming a new genus, and resurrecting two previously supressed taxa. Finally, a new morphological phylogeny for the Iguanodontia is produced using the largest known dataset of 398 characters and 75 taxa using both parsimony and Bayesian workflows, which answers many questions regarding their taxonomy, but also introduces more issues that can only be solved by the discovery of new fossil material, or the taxonomic revision of more specimens.
This thesis gives a thorough overview of the current state of iguanodontian taxonomy, solves some of the most prevalent issues around some key taxa, and suggests future directions for work to continue to reveal the true history of these iconic dinosaurs.
| Date of Award | 13 Sept 2023 |
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| Original language | English |
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| Supervisor | Matthew Wills (Supervisor), Paul M Barrett (Supervisor) & Susannah Maidment (Supervisor) |