The anatomy of <i>Teleocrater Rhadinus</i>, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic)

Bird-line archosaurs (= Avemetatarsalia, the clade containing birds, dinosaurs, pterosaurs, and their kin) originated in the Triassic Period. However, the earliest evolution of this group is poorly documented because fossils are extremely rare and consist mostly of postcrania. Here, we document the osteology of <i>Teleocrater rhadinus</i>, an early avemetatarsalian from the lower portion of the Middle Triassic Lifua Member of the Manda Beds of the Ruhuhu Basin, southwestern Tanzania. Material of <i>Teleocrater rhadinus</i> includes the holotype partial skeleton comprising a single individual, including cervical, trunk, and caudal vertebrae, pectoral, pelvic, forelimb, and hind limb material, and referred specimens representing parts (skull elements, vertebrae, pectoral, pelvic, and limb elements) of at least three other individuals collected from a bonebed. Character states of the skull elements, vertebrae, girdles, and limbs indicate that <i>Teleocrater rhadinus</i> represents the first documented non-ornithodiran avemetatarsalian known from well-preserved, associated material. Furthermore, <i>Teleocrater rhadinus</i> forms part of a newly recognized clade, Aphanosauria, which also contains formerly enigmatic archosaur taxa from across Pangea, including <i>Dongusuchus efremovi</i> from the Middle Triassic of Russia, <i>Yarasuchus deccanensis</i> from the Middle Triassic of India, and <i>Spondylosoma absconditum</i> from the ?Middle Triassic of Brazil. This new clade and other new discoveries from the Middle to Late Triassic elucidate the sequence of character acquisitions at the base of Avemetatarsalia and fill a crucial gap in the understanding of the anatomical transformations that enabled dinosaurs to flourish later in the Mesozoic. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Nesbitt, S. J., R. J. Butler, M. D. Ezcurra, A. J. Charig, and P. M. Barrett. 2018. The anatomy of <i>Teleocrater rhadinus</i>, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic); pp. 142–177 in C. A. Sidor and S. J. Nesbitt (eds.), Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia. Society of Vertebrate Paleontology Memoir 17. Journal of Vertebrate Paleontology 37(6, Supplement).鸟系主龙类（Avemetatarsalia，即包含鸟类、恐龙、翼龙及其近亲的演化支）起源于三叠纪。然而该类群的早期演化历史记录极为匮乏，原因是相关化石极其稀少，且大多为颅后骨骼。 本研究记述了Teleocrater rhadinus——一种产自坦桑尼亚西南部鲁胡胡盆地曼达组中三叠统利夫阿段下部的早期鸟系主龙类——的骨骼解剖学特征。该种的化石材料包括一件正型部分骨架（代表单个个体），包含颈椎、躯干椎、尾椎、肩带、腰带、前肢及后肢骨骼；此外还归入了至少3件其他个体的化石标本，采自同一骨床，包含头骨元素、脊椎、肩带、腰带及肢体骨骼。 头骨元素、脊椎、带骨及肢体的性状特征表明，Teleocrater rhadinus是目前已知首个基于保存完好的关联化石被记述的非鸟颈类主龙类（Ornithodira）鸟系主龙类。此外，Teleocrater rhadinus隶属于一个新确立的隐龙演化支（Aphanosauria），该演化支还包含来自泛大陆（Pangea）各区域的、此前颇具争议的主龙类类群，包括产自俄罗斯中三叠统的Dongusuchus efremovi、印度中三叠统的Yarasuchus deccanensis以及巴西中三叠统（？）的Spondylosoma absconditum。 这一新演化支以及中晚三叠世的其他新发现，阐明了鸟系主龙类基部的性状演化序列，填补了我们对恐龙在中生代后期繁盛所需的解剖学转变认知中的关键空白。 补充数据：本文可免费获取补充材料，网址为www.tandfonline.com/UJVP。 本文引用信息：Nesbitt, S. J.、R. J. Butler、M. D. Ezcurra、A. J. Charig及P. M. Barrett，2018年。《产自坦桑尼亚曼达组利夫阿段（中三叠统）的早期鸟系主龙类Teleocrater rhadinus的解剖学特征》；收录于C. A. Sidor与S. J. Nesbitt主编的《坦桑尼亚与赞比亚三叠纪裂谷盆地的脊椎动物与气候演化》，第142–177页。《脊椎动物古生物学会专刊》第17号，《脊椎动物古生物学杂志》37卷（增刊6）。