The postcranial morphology of the extremely long-necked Tanystropheus hydroides is well-known, but observations of skull morphology were previously limited due to compression of the known specimens. Here we provide a detailed description of the skull of PIMUZ T 2790, including a partial endocast and endosseous labyrinth, based on synchrotron microtomographic data, and compare its morphology to that of other early Archosauromorpha. In many features, such as the wide and flattened snout and the configuration of the temporal and palatal regions, Tanystropheus hydroides differs strongly from other early archosauromorphs. The braincase possesses a combination of derived archosaur traits, such as the presence of a laterosphenoid and the ossification of the lateral wall of the braincase, but also differs from archosauriforms in the morphology of the ventral ramus of the opisthotic, the horizontal orientation of the parabasisphenoid, and the absence of a clearly defined crista prootica. Tanystropheus hydroides was a ram-feeder that likely caught its prey through a laterally directed snapping bite. Although the cranial morphology of other archosauromorph lineages is relatively well-represented, the skulls of most tanystropheid taxa remain poorly understood due to compressed and often fragmentary specimens. The recent descriptions of the skulls of Macrocnemus bassanii and now Tanystropheus hydroides reveal a large cranial disparity in the clade, reflecting wide ecological diversity, and highlighting the importance of non-archosauriform Archosauromorpha to both terrestrial and aquatic ecosystems during the Triassic.

中文翻译：

---

同步加速器显微断层扫描显示的Tanystropheus hydroides (Tanystropheidae, Archosauromorpha) 的颅骨形态

极长颈的 Tanystropheus hydroides 的颅后形态是众所周知的，但由于已知标本的压缩，先前对颅骨形态的观察受到限制。在这里，我们根据同步加速器显微断层扫描数据，详细描述了 PIMUZ T 2790 的头骨，包括部分内模和骨内迷路，并将其形态与其他早期原龙形目进行了比较。在许多特征上，例如宽而扁平的鼻子以及颞部和腭区的构造，Tanystropheus hydroides 与其他早期的原龙形目有很大不同。脑壳具有衍生的主龙特征的组合，例如存在侧蝶骨和脑壳侧壁的骨化，但与主龙类的不同之处还在于反骨的腹侧支的形态、副副蝶骨的水平方向以及没有明确定义的嵴嵴。Tanystropheus hydroides 是一种公羊饲养者，很可能通过横向咬合来捕捉猎物。尽管其他主龙形类谱系的颅骨形态具有相对较好的代表性，但由于标本被压缩且通常是零碎的，大多数tanystropheid 类群的颅骨仍然知之甚少。最近对 Macrocnemus bassanii 和现在的 Tanystropheus hydroides 头骨的描述揭示了进化枝中巨大的头骨差异，反映了广泛的生态多样性，并突出了非主龙形巨龙类在三叠纪期间对陆地和水生生态系统的重要性。