Titanosaurs were the most diverse sauropod group during the Cretaceous period, with most of its diversity being found during the Late Cretaceous. In this work, Tiamat valdecii, gen. et sp. nov. is described, a new species of basal titanosaur prospected from the Açu Formation (Albian–Cenomanian), Potiguar Basin, Ceará state, north-east Brazil. The new taxon is composed by an associated sequence of anterior to middle caudal vertebrae, being diagnosed by four diagnostic features: a marked accessory tuberosity dorsoventrally developed, located on the prezygapophyses; deeply medioventral excavated articulation facets of prezygapophysis and post-zygapophyses articular facets; presence of developed hypantrum–hyposphene articulations; and short middle centra with a well-marked articular facet for the haemal arch. The phylogenetic analysis reveals that Tiamat valdecii was a basal member of Titanosauria. Tiamat is the first species of Early Cretaceous titanosaur known for the Açu Formation. Biomechanical analysis shows that the tuberosity and excavation of the zygapophyses of the middle caudal vertebrae of Tiamat provide greater stability against shear loads in the amphicoelous vertebrae presented; in addition, they allow greater range of lateral movements without affecting the integrity of the joints. These features may have been an evolutionary alternative for the stability of the middle of the caudal vertebral column. The discovery of T. valdecii in the Açu Formation not only increases the known dinosaur diversity for this unit, but also helps us elucidate part of the first titanosaur radiation.

中文翻译：

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巴西西北部的蜥脚类新物种：生物力学和泰坦龙的辐射（蜥脚类：Somphospondyli）

泰坦龙是白垩纪时期最多样化的蜥脚类恐龙，其大部分多样性是在白垩纪晚期发现的。在这项工作中，Tiamat valdecii，gen。等十一月据描述，在巴西东北部塞阿拉州波蒂瓜尔盆地的阿库组（阿尔布阶-塞诺曼阶）中发现了一种新的基础泰坦龙物种。新的分类单元由前尾椎到中尾椎的相关序列组成，通过四个诊断特征进行诊断：背腹发育的明显副结节，位于前关节突上；前关节突和后关节突关节面的深腹内侧挖出的关节面；存在发达的下颌-下颌关节；中间中心较短，有明显的血管弓关节面。系统发育分析表明，Tiamat valdecii 是泰坦龙亚目的基础成员。提亚马特是早白垩世泰坦巨龙的第一个物种，因阿苏地层而闻名。生物力学分析表明，Tiamat 中尾椎骨的结节和关节突的凹陷为所呈现的圆孔椎骨提供了更大的抵抗剪切载荷的稳定性；此外，它们允许更大范围的横向运动而不影响关节的完整性。这些特征可能是尾椎中部稳定性的进化替代。在 Açu 地层中发现 T. valdecii 不仅增加了该单元已知的恐龙多样性，而且还有助于我们阐明第一个泰坦龙辐射的部分内容。