An overview of the appendicular skeletal anatomy of South American titanosaurian sauropods, with definition of a newly recognized clade

Abstract: In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. Here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. The appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of Titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within Titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the ‘Saltasaurinae line,’ which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and Rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.摘要：近二十年来，随着多具新颖且相对完整的标本被发现，泰坦龙类蜥脚类恐龙附肢骨骼中具备系统发育信息价值的解剖特征数量大幅增长。本文综述了南美洲泰坦龙类的附肢骨骼形态，并探讨其对系统发育重建的重要意义。南美洲泰坦龙类的附肢骨骼多样性远超此前的认知，且附肢骨骼的部分区域——如后足（pes）——展现出极为显著的形态变异。泰坦龙类（Titanosauria）以及范围更窄的岩石龙类（Lithostrotia）、萨尔塔龙科（Saltasauridae）的多项共有衍征，均由带骨与四肢的特征构成。尽管萨尔塔龙亚科（Saltasaurinae）、隆科龙类（Lognkosauria）等泰坦龙类支系的系统发育定义已趋于稳定，但近年来的多项分析中，这些支系的分类学内容会因所得到的系统发育拓扑结构不同而发生变化。在泰坦龙类内部，四项近期且基本独立的分析结果均支持存在一支区别于"萨尔塔龙亚科支系"的衍生性泰坦龙类支系，本文将其命名为巨体龙类（Colossosauria）。目前该支系主要包含隆科龙类（Lognkosauria）与林孔龙类（Rinconsauria）中的类群，在探讨泰坦龙类低级分类群间的系统发育关系时具有重要应用价值。