The early origin of Iguanodontia: new insights into the macroevolution, diversity and biogeography of the clade

Iguanodontia (Dinosauria, Ornithischia) is a speciose group of herbivorous dinosaurs that include the famous genus Iguanodon, one of foundational members of the clade Dinosauria. Despite their very long history of research, several aspects of their systematic relationships and their evolutionary history remain somewhat nebulous. There is currently a lack of consensus between different phylogenetic matrices due mainly to: (1) undersampling of postcranial characters; and (2) the absence of several key taxa. We assembled a data matrix from pre-existing datasets, integrating our observations on several overlooked species (mainly from Europe) and extensively sampling cranial and postcranial characters, thereby creating one of the most complete datasets for iguanodontian dinosaurs to date. We performed a series of phylogenetic analyses, employing maximum parsimony and Bayesian inference, and an historical biogeographic analysis. Overall congruent topologies between the two methods recovered, for the first time, a new clade of high-sailed styracosternans here named Ouranosauria. We ran different Bayesian inference analyses, employing morphoclock and fossilized birth–death models. Some of the tip-dated analyses, indicated an Early to Middle Jurassic origin of Iguanodontia during a palaeoclimatically (hyperthermal) and palaeogeographically (continental fragmentation) dynamic context. According to this scenario, the Iguanodontian major radiation could be tracked back to the Pliensbachian–Toarcian, pre-dating by 16 million years the first ichnological evidence attributed to this clade. Furthermore, the diversification of all the major clades occurred by the Late Jurassic, then experienced local extinction events in different areas during the Early Cretaceous. Prior to the Jurassic–Cretaceous transition, iguanodontians spread globally.