Anatomy and phylogenetic affinities of a new silesaurid assemblage from the Carnian beds of south Brazil

New specimens and the reassessment of many silesaurids have recently shed light on the origin and early evolution of dinosaurs and their close relatives. Yet, the group is relatively poorly represented in South America, an area that likely played an important role in dinosaurian origins. Since the discovery of <i>Sacisaurus agudoensis</i> from the Norian Caturrita Formation, only the fragmentary <i>Gamatavus antiquus</i> and <i>Amanasaurus nesbitti</i> have been reported from the Triassic of south Brazil. Here we describe disarticulated silesaurid remains from Waldsanga, one of the most important tetrapod-bearing localities of the Santa Maria Formation, which represent the second Carnian occurrence of the group in Brazil. The postcranial elements exhibit a combination of dinosauromorph symplesiomorphies and silesaurid diagnostic traits, showing that a conservative anatomy is pervasive among early dinosauromorphs. We also conducted a set of exploratory analyses to infer the phylogenetic relations of the new occurrence and the robustness of some of the most recent phylogenetic hypotheses in face of the increasing diversity of Silesauridae. This revealed a rather uncertain evolutionary scenario not only for Silesauridae, but for early dinosauromorphs in general.

新近发现的新标本以及对大量西里龙科（Silesauridae）类群的重新评估，为恐龙及其近缘类群的起源与早期演化研究带来了新的认知。然而，该类群在南美洲的化石记录相对匮乏，而这片区域极可能在恐龙起源进程中发挥了重要作用。
自诺利阶（Norian）卡图里塔组（Caturrita Formation）发现阿瓜多尖齿龙（*Sacisaurus agudoensis*）以来，巴西南部三叠纪地层中仅报道过破碎的古老伽马塔龙（*Gamatavus antiquus*）与内斯比特阿曼龙（*Amanasaurus nesbitti*）两件化石。
本次研究报道了产自圣玛利亚组（Santa Maria Formation）核心产四足动物化石位点之一的瓦尔桑加（Waldsanga）的离散西里龙科化石残骸，这也是巴西境内第二例卡尼阶（Carnian）的西里龙科化石记录。
该类群的颅后骨骼兼具恐龙形类（Dinosauromorpha）的共同原始性状与西里龙科的鉴定特征，表明保守的解剖结构在早期恐龙形类中广泛分布。
我们还开展了一系列探索性分析，以推断此次新发现化石的系统发育关系，并检验当前最新的部分系统发育假说在面对西里龙科日益增加的类群多样性时的稳健性。分析结果显示，不仅西里龙科的演化场景仍较为模糊，早期恐龙形类的整体演化框架亦存在诸多不确定性。