A comprehensive phylogenetic analysis on early ornithischian evolution

Abstract

Resolving the evolutionary relationships of early diverging (‘basal’) ornithischian dinosaurs is a challenging topic in palaeontology, with multiple competing hypotheses on the phylogenetic relationships of heterodontosaurids, ‘hypsilophodontids’, and other early-diverging forms. These hypotheses cannot be directly compared because they are derived from differently constructed datasets (i.e. distinct samples of taxa and characters). This study aims to address these issues by revising and combining the distinct datasets into a single analysis in order to create the most comprehensive dataset for the investigation of the phylogenetic relationships of early-diverging ornithischians. A diphyletic model of Dinosauria is supported, with silesaurs nesting as members of Ornithischia. Heterodontosauridae is resolved as a clade of non-genasaurian ornithischians, rejecting a potential relationship with Marginocephalia. ‘Hypsilophodontid’ taxa span the neornithischian and ornithopod stem, with Thescelosauridae as the sister taxon to Cerapoda. A more restricted Ornithopoda is composed of five main clades: Hypsilophodontidae, Rhabdodontomorpha, Elasmaria, Dryosauridae and Ankylopollexia. Hypsilophodontidae is a valid clade, reduced to two European Barremian taxa. Rhabdodontomorpha does not contain Muttaburrasaurus as originally proposed, but instead expands to include a North American clade formed by Convolosaurus, Iani and Tenontosaurus. Elasmaria contains all non-dryomorph Gondwanan ornithopods, with its members possessing multiple distinct body plans. New results and comparison with previous studies suggest that some members of Dryosauridae are not ‘true dryosaurids’ but various early euiguanodontians that may be more closely related to either Elasmaria or Ankylopollexia. Results group most ‘hypsilophodontids’ in larger clades, significantly reducing the number and extension of ghost lineages throughout all of Neornithischia. These clades also show a degree of endemism, with different lineages present at different continents in the Late Cretaceous. This new phylogenetic analysis unifying previous works will provide a framework for future studies on origins and relations of early diverging ornithischians, and attempting to find stability among the different competing hypotheses.

Keywords:

• Silesauridae
• Heterodontosauridae
• Thyreophora
• Neornithischia
• Ornithopoda
• Marginocephalia

Acknowledgements

We thank the Willi Hennig Society for the free use of the TNT software. This work was carried out with aid of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES 88887.823857/2023-00) to André O. Fonseca and (CAPES 88887.608076/2021-00; 88887.826787/2023-00) to Maurício S. Garcia and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 404095/2021-6; 303034/2022-0; and 406902/2022-4) to Rodrigo T. Müller. Ruairidh J. Duncan acknowledges funding and support from the Australian Government Research Program Scholarship and the Monash University – Museums Victoria PhD Research Scholarship. We thank professors Camila N. Silva and Henrique C. Costa for support at the early stages of the project. We especially thank Clint A. Boyd who has provided invaluable advice and feedback to this project during its development. We thank our friend Amber McCabe who helped us when first developing this project. We thank Benjamin R. Breeden III, Filippo Bertozzo, Paul Barrett, Peter Galton, Phornphen Chanthasit, and Wenhao Wu for access to publications used in this study. We thank Albert Prieto-Márquez, Catherine Forster, David Evans and especially Stephen F. Poropat for sharing additional data on specimens they studied or under their care. We thank the reviewers Caleb Brown and Danial Madzia, and the editors Victoria Arbour and Zerina Johanson for their revision and comments on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2024.2346577.

Associate Editor: Victoria Arbour

Additional information

Funding

We thank the Willi Hennig Society for the free use of the TNT software. This work was carried out with aid of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES 88887.823857/2023-00) to André O. Fonseca and (CAPES 88887.608076/2021-00; 88887.826787/2023-00) to Maurício S. Garcia and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 404095/2021-6; 303034/2022-0; and 406902/2022-4) to Rodrigo T. Müller. Ruairidh J. Duncan acknowledges funding and support from the Australian Government Research Program Scholarship and the Monash University – Museums Victoria PhD Research Scholarship. We thank professors Camila N. Silva and Henrique C. Costa for support at the early stages of the project. We especially thank Clint A. Boyd who has provided invaluable advice and feedback to this project during its development. We thank our friend Amber McCabe who helped us when first developing this project. We thank Benjamin R. Breeden III, Filippo Bertozzo, Paul Barrett, Peter Galton, Phornphen Chanthasit, and Wenhao Wu for access to publications used in this study. We thank Albert Prieto-Márquez, Catherine Forster, David Evans and especially Stephen F. Poropat for sharing additional data on specimens they studied or under their care. We thank the reviewers Caleb Brown and Danial Madzia, and the editors Victoria Arbour and Zerina Johanson for their revision and comments on the manuscript.