The origin and evolutionary relationships of ornithischian dinosaurs are topics that have undergone a series of substantial revisions. At present there are several competing hypotheses concerning the relationship between Ornithischia and the other principal clades of Dinosauria. 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. In contrast, other hypotheses have placed conventionally Triassic dinosauromorph (stem-lineage Dinosauria) taxa within the clade Ornithischia. 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. 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. 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). 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. The present article addresses these latter issues by expansion and re-analysis of the original dataset. 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 overall topology of the consensus tree remains but little changed from the original analysis, despite the addition of new taxa and characters. 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. 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. We also erect Parapredentata as a more exclusive subclade in Ornithischia. 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. 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.

中文翻译：

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鸟臀目（Archosauria：Dinosauria）系统发育假说的分类学、古生物学和进化意义

鸟臀目恐龙的起源和进化关系是经过一系列实质性修改的话题。目前，关于鸟臀目和恐龙的其他主要分支之间的关系有几个相互竞争的假设。一些假设在恐龙中提出了一个树形拓扑结构，这意味着鸟臀目（其代表首次在赫坦阶中明确出现）的“幽灵谱系”延伸到三叠纪的大部分时间。相比之下，其他假设将传统的三叠纪恐龙类（干系恐龙）分类群置于进化枝鸟臀目中。最近，一项大规模的系统发育分析发现了一系列被称为“西里龙科”的分类群，作为通向鸟臀目进化枝的分支上的分类群（在本文中使用非正式术语 silesaurs 或 silesaurians 指代）的并系组合。后一种关系假设将解释三叠纪鸟臀目明显缺失的原因，因为干系鸟臀目（本文中的西雷龙）完全是三叠纪的。然而，产生这种新拓扑结构的分析使用了一个数据集，该数据集以其原始形式不包括鸟臀目（sensu lato）的所有早期代表，并且没有包含所有被建议将鸟臀目与其他恐龙联合起来的解剖特征进化枝（兽脚亚目和蜥脚类动物）。最初的研究也没有继续扩展一些重要的分类，将一组并系的 silesaurs 与进化枝 Ornithischia 联系起来的拓扑学的古生物学和进化意义。本文通过对原始数据集的扩展和重新分析来解决后面的这些问题。结果进一步支持了以下假设，即 silesaurs 包括鸟臀目茎上的分类群的并系群，并且连续的 silesaur 分类群在一个可被描述为“传统”鸟臀目的组装过程中通过遗传方式获得解剖特征。尽管添加了新的分类群和特征，但共识树的整体拓扑结构与原始分析相比几乎没有变化。为树的这一区域提供稳定性并保留最重要的相关分类名称，我们建议修订与这种新拓扑结构一致的鸟臀目分类框架。我们为整个群保留了鸟臀目的名称（传统的鸟臀目及其茎干谱系），同时我们恢复了最初由 Richard Owen 提出的名称，Prionodontia（= '粗边牙齿'）用于仅包含所谓的传统的进化枝鸟臀目（=“鸟臀”）恐龙。我们还将 Parapredentata 竖立为鸟臀目中更独特的亚群。随着进一步分析和新数据不断完善和重塑树，这种新颖的分类框架旨在为鸟臀目和恐龙提供系统发育的清晰度和一定程度的稳定性。