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| A Comprehensive Phylogenetic Analysis on early Ornithischian Evolution in Fonseca, Reid, Venner, Duncan, Garcia & Müller, 2024. |
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
André O. Fonseca, Iain J. Reid, Alexander Venner, Ruairidh J. Duncan, Mauricio S. Garcia and Rodrigo T. Müller. 2024. A Comprehensive Phylogenetic Analysis on early Ornithischian Evolution. Journal of Systematic Palaeontology. 22(1); 2346577. DOI: 10.1080/14772019.2024.2346577
