A basal tetanuran theropod dinosaur from the Middle Jurassic of Argentina: implications for the early evolution of tetanuran theropods

兽脚类恐龙是中生代脊椎动物动物群中最显著的组成部分之一，以鸟类的形式，约占现代四足动物的三分之一。最近的研究表明，兽足类在侏罗纪经历了一次爆炸性的辐射，最重要的谱系是在这段时间建立的。在此期间辐射的主要谱系是破伤风类，其中包括著名的化石形式，如异特龙，暴龙或伶盗龙，但也包括鸟类。Tetanurans最早出现在中侏罗世早期，到该时期结束时，所有主要的谱系都建立起来了。然而，特别是中侏罗世兽脚类恐龙的记录极其贫乏，大多数基本的破伤风类群由非常不完整的材料代表。因此，基础破伤风之间的早期进化和系统发育相互关系仍然知之甚少。最近在阿根廷丘布特省中侏罗世早期(Aalenian-Bajocian)进行的野外调查发现了部分兽脚类骨骼，包括几乎完整的头骨、骶前脊柱、前肢和部分后肢。该标本代表了从中侏罗世发现的最完整的基础破伤风，并显示了独特的特征组合，包括迄今被认为是不同支系甚至不同种类的基础破伤风的特征。因此，本项目的目标是对这种新的基础破伤风进行详细的描述和分析，以评估其对我们了解基础破伤风演变的影响。我们将详细描述和记录新的分类群，并详细描述一个大型的系统发育数据集，包括最近发表的几个基本兽脚亚目的系统发育矩阵。新分类单元的加入和对这一矩阵的分析将导致对基础破伤风的相互关系以及这一重要兽脚类谱系基础上的特征分布和同质性水平的新见解。

Theropod dinosaurs represent one of the most conspicuous components of Mesozoic vertebrate faunas and, in the form of birds, account for approximately one third of modern tetrapods. Recent research has demonstrated that theropods underwent an explosive radiation during the Jurassic, and most important lineages were established during this time. The main lineage radiating during this period are the tetanurans, which include well-known fossil forms, such as Allosaurus, Tyrannosaurus or Velociraptor, but also the birds. Tetanurans first appear in the early Middle Jurassic, and by the end of the period, all major lineages are established. However, especially the Middle Jurassic record of theropod dinosaurs is extremely poor, and most basal tetanuran taxa are represented by very incomplete material. Consequently, the early evolution and the phylogenetic interrelationships between basal tetanurans are still poorly understood. Recent fieldwork in the early Middle Jurassic (Aalenian-Bajocian) of Chubut Province, Argentina, resulted in the discovery of a partial theropod skeleton, including an almost complete skull, presacral vertebral column, forelimbs, and partial hindlimbs. This specimen represents the most complete basal tetanuran recovered from the Middle Jurassic and shows a unique combination of characters, including features that were hitherto considered apomorphic for different clades or even different species of basal tetanurans. The objective of the current project is thus a detailed description and analysis of this new basal tetanuran to evaluate its impact on our understanding of basal tetanuran evolution. We will describe and document the new taxon in detail and elaborate a large phylogenetic dataset, including several recently published phylogenetic matrices for basal theropods. The inclusion of the new taxon and the analysis of this matrix will result in new insights into the interrelationships of basal tetanurans as well as character distribution and homoplasy levels at the base of this important theropod lineage.