A second species of <i>Eucnemesaurus</i> Van Hoepen, 1920 (Dinosauria, Sauropodomorpha): new information on the diversity and evolution of the sauropodomorph fauna of South Africa's lower Elliot Formation (latest Triassic)

ABSTRACTThe Late Triassic–Early Jurassic Elliot Formation of South Africa is one of the most important geological formations worldwide for understanding the early evolution of sauropodomorph dinosaurs. However, many of the taxa currently recognized as valid within its lower strata remain either poorly understood, vaguely diagnosed, or both. The recent discovery of an articulated partial skeleton of a single individual of the enigmatic lower Elliot genus <i>Eucnemesaurus</i> provides an important opportunity to expand our understanding of the anatomy and phylogeny of this poorly known taxon. A comprehensive investigation of the morphological relationships of this new specimen identified key features, pertaining primarily to the femoral shaft and distal tibia, which distinguish it from the only other previously named species of <i>Eucnemesaurus—E. fortis</i>. A new species, <i>E. entaxonis</i>, is erected within which to accommodate it. A cladistic analysis confirms the monophyly of <i>Eucnemesaurus</i>, as well as its continued inclusion within the low-diversity ‘Riojasauridae.’ Nonetheless, this result highlights continued uncertainties regarding the constituency of the <i>Riojasaurus</i> hypodigm. The relatively robust pedal architecture of <i>E. entaxonis</i> suggests an unexpectedly early experiment in a slower, subgraviportal form of locomotion within Late Triassic basal Massopoda, whereas the intriguing mosaic of plesiomorphic and derived characters evident in <i>E. entaxonis</i> raises questions regarding the hypothesized population dynamics of the basal-most sauropodomorph taxa of the lower Elliot Formation. This latter concern has particular bearing on newly observed inconsistencies in the prevailing hypodigms of other lower Elliot basal sauropodomorph taxa such as <i>Melanorosaurus</i>.http://zoobank.org/urn:lsid:zoobank.org:pub:68A7F233-2424-469E-A008-442C4E04B02FSUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP摘要 南非晚三叠世至早侏罗世的埃利奥特组（Elliot Formation）是全球范围内研究蜥脚形类恐龙（sauropodomorph dinosaurs）早期演化的重要地质地层之一。然而，目前其下部地层中被认定为有效的多数类群，要么研究程度不足，要么诊断模糊，抑或两者兼具。近期发现的一具关联保存的神秘埃利奥特下部地层优颌龙属（Eucnemesaurus）个体的部分骨骼，为我们深化对这一鲜为人知类群的解剖学与系统发育学认知提供了关键契机。 针对该新标本的形态学亲缘关系开展的综合研究，识别出主要关联股骨骨干与胫骨远端的关键特征，这些特征可将其与此前唯一命名的优颌龙属物种——强壮优颌龙（E. fortis）区分开来。据此，我们建立新种恩塔克萨斯优颌龙（E. entaxonis）以容纳该标本。 分支系统学分析（cladistic analysis）证实了优颌龙属的单系性（monophyly），同时确认其仍隶属于低多样性的里奥哈龙科（Riojasauridae）。尽管如此，该分析结果仍凸显出里奥哈龙属（Riojasaurus）的标本集合在组成范畴上尚存不确定性。 恩塔克萨斯优颌龙相对粗壮的足部骨骼结构，暗示晚三叠世基底大脚类（Massopoda）中存在一次出乎意料的早期尝试，即演化出更为缓慢的亚重载型运动模式；而该物种所呈现的兼具祖征（plesiomorphic）与衍征（derived）的有趣镶嵌特征，则对埃利奥特组下部地层最基底蜥脚形类类群的推测种群动态提出了疑问。这一问题尤其与黑瑞龙属（Melanorosaurus）等其他埃利奥特下部地层基底蜥脚形类类群的主流标本集合中新近观测到的不一致性相关。 http://zoobank.org/urn:lsid:zoobank.org:pub:68A7F233-2424-469E-A008-442C4E04B02F 补充数据——本文的补充材料可于www.tandfonline.com/UJVP免费获取。

搜集汇总

背景与挑战

背景概述

该数据集是关于南非晚三叠世下Elliot Formation中蜥脚类恐龙演化多样性的古生物学研究。它基于新发现的Eucnemesaurus属部分骨架，建立了新物种E. entaxonis，并通过形态学和系统发育分析扩展了对该属的理解，同时探讨了早期运动方式的演化和相关分类单元的问题。