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Anatomical phenomena definition9/18/2023 ![]() ![]() Ornithischia has been long considered one of the two fundamental components of the Dinosauria – the other being Saurischia – with the arrangement of their pelvic bones being used as the primary criterion for this division, as implied by their names ( Seeley, 1888 Charig, 1972, 1976 Bakker & Galton, 1974 Novas, 1996 see Fig. The data presented in this study represent a stage in our attempt to establish an early dinosaur dataset in which character definitions and character scores are agreed upon and used consistently.Īnagenesis, dentition, Dinosauromorpha, herbivory, Heterodontosauridae, Jurassic, Neornithischia, postcranial anatomy, Prionodontia, silesaurs, systematics, Thyreophora, Triassic INTRODUCTION This novel taxonomic framework is intended to provide phylogenetic clarity and a degree of stability in Ornithischia and Dinosauria as further analyses and new data continue to refine and re-shape the tree. We also erect Parapredentata as a more exclusive subclade in Ornithischia. We retain the name Ornithischia for the total-group (traditional Ornithischia and its stem-lineage), while we resuscitate a name originally proposed by Richard Owen, Prionodontia (= ‘coarse edged teeth’) for the clade containing only the so-called traditional ornithischian (= ‘bird-hipped’) dinosaurs. To provide stability to this area of the tree and to preserve the most important of the relevant taxonomic names, we suggest a revised taxonomic framework for ornithischians that is consistent with this new topology. The overall topology of the consensus tree remains but little changed from the original analysis, despite the addition of new taxa and characters. ![]() The results find further support for the hypothesis that silesaurs comprise a paraphyletic grouping of taxa on the stem of Ornithischia and that successive silesaur taxa acquire anatomical characters anagenetically in a process that culminates in the assembly of what may be described as a ‘traditional’ ornithischian. The present article addresses these latter issues by expansion and re-analysis of the original dataset. Nor did the initial study go on to expand upon some important taxonomic, palaeobiological and evolutionary implications of a topology that links a paraphyletic array of silesaurs to the clade Ornithischia. However, the analysis that produced this novel topology used a dataset that, in its original form, did not include all early representatives of Ornithischia ( sensu lato), and did not incorporate all the anatomical characters that have been suggested to unite Ornithischia with other dinosaurian clades (Theropoda and Sauropodomorpha). This latter hypothesis of relationships would account for the apparent absence of Triassic ornithischians, because stem-lineage ornithischians (silesaurs in this article) are exclusively Triassic. Recently, a large-scale phylogenetic analysis recovered an array of taxa, known as ‘silesaurids’, as a paraphyletic assemblage of taxa (referred to in this article using the informal terms silesaurs or silesaurians) on the branch leading to the clade Ornithischia. In contrast, other hypotheses have placed conventionally Triassic dinosauromorph (stem-lineage Dinosauria) taxa within the clade Ornithischia. ![]() Some hypotheses have posited a tree topology within Dinosauria that imply a ‘ghost-lineage’ for Ornithischia (whose representatives make their first unambiguous appearance in the Hettangian) that extends through a substantial portion of Triassic time. At present there are several competing hypotheses concerning the relationship between Ornithischia and the other principal clades of Dinosauria. The origin and evolutionary relationships of ornithischian dinosaurs are topics that have undergone a series of substantial revisions. ![]()
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