ABSTRACT

The titanosaurian sauropod dinosaur Savannasaurus elliottorum is represented by a partial postcranial skeleton from the lower Upper Cretaceous (Cenomanian–lowermost Turonian) Winton Formation of Queensland, northeast Australia. Here, we present a detailed description of this specimen, as well as an emended diagnosis for this titanosaur. Savannasaurus elliottorum displays numerous character states that are generally regarded as plesiomorphic for Titanosauria, as well as several traits that are often regarded as apomorphic of that clade or a less inclusive subset thereof. Several features of Savannasaurus support a close relationship with the coeval Diamantinasaurus matildae, and this clade appears to occupy an early-branching position within Titanosauria. Relative to body size, the thoracic and abdominal breadth of Savannasaurus is greater than that seen in giant titanosaurs such as the contemporaneous South American lognkosaurians; however, this relative breadth is not quite as extreme as that of the small-bodied latest Cretaceous saltasaurines, or Opisthocoelicaudia skarzynskii. The possible advantages engendered by the barrel-shaped thorax, robust limbs, wide-gauge gait, and lack of hyposphene-hypantrum articulations are explored, and it is hypothesized that these traits were positively selected by the wet, temperate floodplain environment in which Savannasaurus lived. Greater stability and flexibility might have reduced the risk of bogging, and/or facilitated more expedient self-extraction from muddy waterholes. Similar environmental pressures acting upon other titanosaurian taxa or clades elsewhere might have led to the repeated independent development, or accentuation, of the bauplan regarded as ‘typical’ for the clade Titanosauria. This would explain the many observed convergences between Savannasaurus and Diamantinasaurus, and Saltasauridae.

摘要

泰坦蜥脚类蜥脚类恐龙稀树沙棘以澳大利亚东北部昆士兰州上白垩统（西诺曼尼亚至最低的突厥人）温顿组的下颅骨骨架为代表。在这里，我们介绍了该标本的详细说明，以及对该钛龙的修正诊断。稀疏沙棘显示出许多特征状态，这些特征通常被认为是泰坦龙的多形性，以及几个特征，通常被认为是该进化枝或其包容性较弱的亚种。稀树草原的几个特征与中世纪的Diamantinasaurus matildae有密切的关系，并且这个分支似乎在Titanosauria中占据了一个早期分支的位置。相对于身体大小，胸，腹宽Savannasaurus是比巨人泰坦巨龙，如当时的南美lognkosaurians看到更大; 但是，这种相对宽度并不像最近的小白垩纪盐藻或Opishocoelicaudia skarzynskii那样极端。由筒状胸部主义及其可能的优点，健壮四肢，宽轨步态，并且缺乏hyposphene-hypantrum关节的进行了探索，它是假设，这些性状呈正通过湿法，温带漫滩环境来选择，其中Savannasaurus住了 更高的稳定性和灵活性可能降低了堵塞的风险，和/或有助于从泥泞的水坑中更方便地进行自我提取。类似的环境压力作用于其他泰坦龙类群或其他进化枝上的进化枝，也可能导致被认为是泰坦巨蜥科进化枝“典型”的鲍兰的反复独立发育或加重。这将解释沙文龙和Diamantinasaurus以及Saltasauridae之间的许多已观察到的收敛。